It's much too late. If he said that, conservative voters would look at his personal history and his voting record and say, "No way, Jose." He could never be trusted to do those things. But he would alienate a ton of his liberal supporters. They wouldn't really believe him either, but it would be too much for them to take. They'd vote for Nader, as a write-in candidate if necessary.
I agree. He has flipped and flopped so many times I don't even know if he himself knows what he believes.