Well, if he has difficulty chewing I think you can only let him have what he likes. Remember that the finre content of hay is just as much about them wearing their teeth and expending energy chewing and digesting, so controlling weight, as it is about fibre in the gut. If he is pooing normally on what he eats then I would be inclined to leave well alone, or try subtituting a new pellet by increasing its proportion in his rations over a week to 10 days so his gut has time to adjust to the new pellet. Why not get the smallest packet you can and try him out?
Adam