When my goats ate honeysuckle, which can cause stomach upset and diarrhoea, I was advised by the vet to feed only hay for 3 days and give them pro-rumen, this is a ruminant probiotic. On day 3 Waffle had a very upset tummy, but was bright within herself, she was the only one to show any symtoms though, so I would guess it would be a good idea to do the same with your bunny, hay and biolapis or fibreplex, to "dilute" any ill affects. Would you be able to put some slabs under a run for him, so he can get out but not eat the weeds.
By the by, I had a terrible problem finding out if honeysuckle was poisonous to goats and ended up calling the vet on a sunday, who then called the London poisons unit. The internet said it was good, mildy toxic, toxic to highly toxic, on different sites, you can't trust what you read.
