Who can replace Kerry as Obama's debate practice sparring partner?

I've got an idea:

Bill Clinton. But even if he would do it, Obama shouldn’t trust him. If somehow he could, I don’t think Obama would like sharing even the practice stage with the man who out-shone him at the convention and who would easily best him at debate. And yet, with 2 more public humiliations in the offing, he’s got to do something. If he’s really desperate, there could be a world crisis of some sort that forces him to cancel the remaining debates.