Is there anywhere out of the group he can be? Even at the dark end of the hall or something? I have napped a kid in the bathroom (legs in bathroom, head out in hallway) for 1 day b/c he simply didnt get the leaving other people alone concept. Removing this kid from the group and therefore not giving him the control might help him learn he would rather function normally than be on his own. I have also let other kids have "special" privledges like reading one to one with me when they go to bed or taking 2 books to bed so the difficult ones are encouraged to be good.
Also, call him out to mom/dad about it. One mom in the past said she would pick her daughter up if she disrupted others at nap and would have consequences for her for not being able to function with the group. Once her daughter knew this she never, never, tried any nonsense with me again. Mom told me she explained the consequence would be that the daughter would do chores at home until she came to pick up her brother at the normal pick up time, then the daughter would go straight to bed (tired from all the chorse and not napping I suppose
) while the boy was allowed to choose his own dinner and play whatever he wanted with mom at night. I guess if the parents mean business at home one talking to might straighten him up.