If hes not a 'quick recovery' guy you shouldn't really push him, this could cause arm problems. If i had to recommend anything it would be to run/sweat a lot after the day he throws. I wrote an
article on starting pitchers in season workout, but you need to realize that pitchers in season workouts are very personalized and can vary. Overall, just make sure your son is in shape (cardio, plyos, throwing and weight lifting during the off season) and his recovery time should shorten the better shape he is in