In two words: He can't.
McCain is losing because his campaign has been all over the damn place, which undercuts his core value proposition ("You'll always know where I stand, my friends.") and scares voters in a time of crisis. Even if he were to pick one of his many tracks and stick with it, 9 days is far too short a stretch of time to change the impression McCain has spent the last 6 months creating in the minds of voters.
He can play the woulda, coulda, shoulda game, but unless he's got a time machine, he's has no good options left.