The expression "more than one can help" is a literal absurdity. It means exactly the opposite of what it says. "I won't be longer than I can help" means "I won't be longer than is unavoidable ", that is to say, longer than I can't help. But it is good English idiom.
They will not respect more than they can help treaties exacted from them under duress. (Winston Churchill The Gathering Storm).
Writers who find the absurdity of the phrase more than they can stomach can always write "more than they must" instead.