Have you had a talk to an ABA counsellor about this - 1800 Mum2Mum ?
It will probably resolve itself as he gets bigger and better able to deal with the milk flow.

Try feeding with you lying on your side and him lying on his side on a big towel - that way if the issue is that your milk shoots out faster than he would like he won't feel like he is choking, and he can just let the excess dribble out of his mouth.