I think the best you can do is keep him hydrated. Add water to his canned food so it is soupy and see if he will eat that. There is an emergency kitten formula you can make to help give them a boost, I don't know if he is at that point, but it is with karo syrup and goats milk, you will have to search the forum for the recipe. It is on here a bunch, or maybe someone else can link you to it.