You absolutely cannot do this. It is illegal. If it is discovered, your son will have all his acceptances rescinded. Colleges can and do use the national clearinghouse database to see where students are registered for college. If he is caught he will also have a black mark against his name. He has to decide like everyone else by May 1. He doesn’t get special rules just for him and everyone else has to go by the rules.
This post seems nearly identical to a post from yesterday, which seems to have disappeared.