My Monty does this also. Dr Bicks suggested using smooth, round edge river rocks that are too large for him to get in his mouth. It has slowed him down.
I also like the idea of splitting up his meal. I have also given Monty some cut up apple (pealed of course, oh he's not spoiled
) and waited about 10 - 15 minutes then feeding him. I noticed he eats slower when I've done this.