How old is he? I hand raised a pair of kittens that were a little older, but not by much.
Get a medicine dropper and kitten formula, and have the mixture at slightly warmer than luke--like you would feed a human baby. You will be feeding several times a day and at night. But if he sleeps let him sleep. I used a hot water bottle covered with a towel to keep my kits warm--but I had two, and that helped. I also kept the box they were in right by my bed. You will have to use a warm wet washcloth to bathe his face, body, and especially the rear end. Gentle wiping across the genital area is what will stimulate him to go to the bathroom.
You will have to change everything every day or so, but he will get used to it. Just keep him warm and don't let him get chilled. Dit (wo not feed more than one or two medicine droppers--or small needle syringes (w/o needle) until you see how he tolerates it. Later, you can start adding baby farina to the formula. Then you get to introduce your kitten to the concept of a bath....