Imo, I would try rehydrating him first with warm water. I would sit him in a shallow tub with just enough water to cover the belly scales. See if you can get him to drink the water by just monitoring him while he is in the shallow tub. Trying to force feed or assist feed before the animal is somewhat rehydrated is not the best procedure. Snakes absorb fluids through the cloaca so by just placing him in the warm water you are giving therapeutic fluid replacement that will help some. If he drinks the water then that is a added plus! Stay in peace and not pieces. Good luck.