Just in case you haven't tried any of these things...
Could you give him half a piece of bread half an hour before dinner (or something similar) just so that he doesn't feel so hungry? I think it takes the body something like 30 minutes to realise it is full - so it might help him to not feel like he needs to shove the food down so quickly

. Also a cup of milk or water earlier on might help too.
Could you encourage him to chat to you while you are all eating together - so that he stops every few mouthfuls?
Could you give him a small portion and then he can have a bit more when he's finished it - just to stagger his meal?
xx