I've seen the really broad contracts where basically anything you do while employed by them is theirs, but OP said that it would not be out of the question that

I've seen the really broad contracts where basically anything you do while employed by them is theirs, but OP said that it would not be out of the question that the boss could get a cut of the earnings from music. Is there any place in the U.S. where a judge would enforce such a contract to that degree?