OK, I know it is cheating, but rabbits seem to be a sucker for cereal hays, especially oat hay. Cereal hays are lower in calcium and higher in phosphorous than grass hays because of the seed head, so it helps if they also like legume hays such as clover, alfalfa etc, or at least wild plant forage which is normally high in calcium, but it is at least a start.
If you PM me with your mailing address I'll send you a free sample pack of hay including oat hay, orchard grass and timothy; forage including spelt and wheat cereal grass hay, young green barley grass. alfalfa and various herbs.
Feed the oat hay first, then the cereal grass hays and young barley before moving on to the herbs, alfalfa and then the grass hays.
There's not as much indigestible fibre in veggies but they play a role in encouraging variety, so I'll send you some Very Veggie as well. Don't worry if he doesn't eat everything, the main thing is to get him brave enough to try different things.