The only other thing that springs to mind is studious attention to attachment. We often get a bit slack about it as they get older - he should not be able to bite if he's on 'right'. (ETA - oh, MR already said all this). I think efjay and gigi had some good advice on this topic...

DS did this to me when he was about 1. There were 2 kinds of bites. The end-of-feed nip, which was pretty easy to pick and avoid with a bit of practice, and the all-out, all-of-a-sudden clampdown. It went on for a while. I would stop feeding if he bit me, and no more till the next feed. The last time he did it he drew blood and I told him no more feeds period (but relented at bed time). I guess he finally got the message

Anyway, I can completely understand not wanting to feed like this. I hope he gets the message soon.