In a way, I kind of hope McCain doesn't show up, just to see what Saturday Night Live does with it.
They could have Obama on stage just twiddling his thumbs waiting for McCain to show up. A minute or two of silence passes, and the moderator of the debates says, "Sen. Obama, it seems Sen. McCain is a no-show...Is there anything you'd like to say at this time?"
[cut to Sen. Obama, looking up from his thumbtwiddling]
"Yes, thank you...Live from New York..."