Are you giving him papaya or pineapple? Both have enzymes that help to break down hairballs/pass 'em through.

Piper doesn't like pineapple so he gets one papaya tablet twice a week. (The vet said it's one tablet per 5lbs of bunny.) Those are found in the vitamin section.

Soph didn't like papaya so I bought her Dole pineapple juice. (You can either buy fresh pineapple or canned. If it's canned, make sure there's no added sugar/sweetner.) I *think* the weekly dose on that is 2 tblsp per 5lbs of bunny -- I just set some out and let her drink all she wanted in a 4-5 min period.

Also, pina colada yogurt is good to use as a healthy treat. Again, it's a weekly thing of 1-2 tblsp per 5lbs of bunny. (And don't get the non-fat kind, get the "regular.")

Try a small curry comb (aka zoom groom) or a shedding blade to help w/ the loose hair.

I sometimes get disapproving looks/comments because I bathe my rabbits but it's also an option. I wouldn't recommend doing it regularly because they can get dry skin EASILY. If you go this route, make sure the shampoo is bunny safe (I use Bunny Bath).