need help with a stuck bonding pair

I am trying to bond my 3y/o fixed female Thumper with our 1y/o fixed male Jr. Thumper recently lost her bonded partner to old age and was still grieving for him so we decided to bond her with Jr so she wouldn't have to be alone and because jr has needed company for a while but we hadn't managed to bond him with any of our other rabbits. Now its down to just the two of them so they are all they have.
Its very clear Thumper desperately wants to bond with Jr and be together with him as she's missing her old partner, but we're having problems getting them to communicate properly. I should mention that jr, being very young, is very bouncy and energetic and kinda a scatterbrain, sweet though he is he can be completely clueless. His only bunny to bunny interaction has been with his mother until he was 3 weeks old and she started to attack him and we had to separate them for his safety, and my ex decided to introduce him to some other baby bunnies when i was not around and they attacked him as well. Consequently he does not speak rabbit very well and seems to only understand aggressive bunny language. To avoid being attacked his response is often to lay very still with his head down and not move for anything until he thinks its safe then he attempts to look for teats on Thumper, which (her not being his mother) doesn't please her much. He doesn't seem like a very dominant type rabbit so i don't think he's requesting grooming out of a desire to be on top, he just acts like a frightened baby.
Thumper on the other hand wants to be the dominant one, she has already humped him a couple times to make this clear and he does not resist or get aggressive in any way when she does this. When they meet they usually end up nose to nose both with their head down in the 'groom me now' pose and thumper always ends up giving in first and grooming him for a while then will request again. He has never groomed her and we have been trying for a couple weeks to figure out how to get him to understand that's what she wants. It seems to us like if he could groom her she would be happy to bond the rest of the way and they could make the transition into their play area. we have been doing cage switching for a month before we started bonding them in a neutral area. She gets offended when he refuses to groom her or if he hops by without acknowledging her (we are not surprised and its almost painful to watch him make the same mistakes over and over) and so she will chase him off with a quick nip and he will then spend the next 10min sitting on the other side of the bathroom staring fearfully at her wondering why she attacked him. This happens over and over since we started. i was very encouraged by her willingness to groom him (as a diva bunny i can only put this down to her grief over losing her partner) and to forgive him again and again when he unknowingly insults her. She will often approach him, ask for grooming and when he ignores she pointedly turns her back on him while staying in reach to say 'hey, you are insulting me, fix it' but he doesn't seem to understand or know what to do to fix things.
I should also mention at this point that i am doing this bond long distance, my mother is in the room with the rabbits and i am helping on skype (this is due to a complicated series of events in my personal life separating me from my rabbits and my mother in one go) she is in the USA and i am in England so there is no way for me to reach her to help. If i was with her i might try stressing them in a car ride since both of them hate car rides and associate them with either the vet (both of them having been fixed last year) or a change of home, but as my mother is alone she cannot be both driving and in the back with the buns. I have suggested putting them in a box on top of her washing machine but apparently she just got a new one which is very quiet and doesn't shake much (her old one would have been ideal this thing made a noise that used to scare jr even when he wasn't near it)
I don't want to put them under more stress than necessary, but i really want them to be friends, especially as i can see thumper wants so badly to not be alone now she's enjoyed the company of her old partner (who was, i should mention, also male but very laid back and slow moving unlike jr who is practically polar opposite).
during bonding sessions, thumper is willing to eat with him around and has even groomed herself. she has not yet been relaxed enough to lay down (barring grooming invites). jr on the other hand, will eat, groom and lie down with him around, but they are not doing these behaviours 'together' they are doing them from opposite sides of the room. the closest we came was a few days ago jr lay down about two feet from her while she was dozing on her feet and they stayed that way for about 10min before he jumped up and she got startled. we tried using a smear of jam on thumpers forehead to encourage him to try grooming her, all that happened was she got sticky and never got groomed. my heart aches for her to be suddenly alone and stuck with a clueless babylike bunny who is not like her old partner.
any suggestions or insight into what we should/could do next to help these two become life mates would be great. We have even built them a very large cage with platforms at different heights (offset for safety) which they love and we would love them to be able to share it (at the same time that is, we are using that one in our cage switching)
thanks in advance.

Have you tried just putting them together in a cage and leaving them, as long as they don't attack one another. The problem with cage switching, if one of the rabbits is very territorial, he/she is going to assume ownership of both cages. This then makes it difficult to bond them in either of the cages. As you don't mention that they are attacking one another then I can't see a problem? Rabbits communicate in their own ways and even though you had to separate him from his Mother at 3 weeks, he will still have the basic instincts in him.
The reason he was attacked by the other baby rabbits is that even at that young age they knew he didn't belong to their family.

Not all rabbits groom one another so don't attach too much importance to it. As long as they cohabit peacefully then you have 2 happy rabbits. Rabbits groom each other when it is quiet and private quite often.

well if thumper didn't care much that he didn't groom her, i would not worry, but she gets upset and drives him off when he doesn't groom her. i keep hoping he will just groom her even for a second to make her happy. they have had a few little tussles but nothing that threatened to do more than leave a small chunk of fur on the floor and two rabbits on either end of the room staring at one another. i am worried that putting them in the same cage would only provoke thumpers territorial nature and cause her to do more than just nip at him to teach him a lesson. they don't seem to mind sharing the cages so far, they have kept them clean and use the litter trays in the bottom. there has been no sign of pooping or peeing to mark against the other bunny. the exercise area for the most part stays clean too, so i don't think they see one another as a threat or dislike one another, thumper just keeps getting offended and annoyed by his 'rude' behaviour toward her.

I don't know if this is something that will help, or even work at all for your bun, but with some of my rabbits when I scratch their hind end on the sides while I'm grooming, they compulsively start licking anything around them. It might be the floor or another rabbit. If it works with Jr maybe it will help jumpstart the grooming.

Maybe also letting them out to play together in a larger area that they aren't in very often, so they are busy investigating the area and aren't so concerned with each other, might help them get used to each other better. I know with bonding it's usually better to start off with small spaces, but sometimes when things aren't working, it helps to try something different.

Did you attempt to bond in a completely neutral area - ie where neither of the rabbits have been?

Yes we used a neutral area. a bathroom neither rabbit had ever seen. cat smell around too which made them a bit nervous at first (dont worry cats were no where near them while we had them upstairs).

thanks for the suggestion, if hes calm enough that might work to trick him into it, if it appeases her then thats all that matters, i have a feeling he will enjoy grooming her once he tries it.

I have heard of a trick where you smear some banana on the head of the bunny you want groomed. I've never tried it since it doesn't deal with the underlying problem. But if you think he just needs a kick start it might be worth a go?

Good luck!