Let me humbly suggest that Nick's pledge idea has a flaw. Sure, you can try to compel Democratic superdelegates to vote for whichever candidate arrives at the convention with the most delegates. But few will sign such a pledge, whether or not the Obama and Clinton campaign ask them to do so. Why give up a privilege? Especially when--here's the real issue--outside events might change the landscape.
The last big-state primary (Pennsylvania) occurs on April 22 and the primaries altogether end on June 3. What if in between those dates and the Democratic convention, which opens on August 25, something happens? Maybe Barack Obama is in the lead, and a news report discloses he once sold dope to lobbyists for a health insurance industry. Maybe Hillary Clinton is ahead, and it turns out she did hide legal records during the Whitewater investigation and plotted with her husband to kill their political enemies. In such instances, superdelegates might want to mount a course correction.
Admittedly, these are extreme examples. But there could be other less extreme circumstances in which it would make sense for the superdelegates to reconsider the popular will. As I noted, my hunch is that superdelegates will not willy-nilly vote to hand the nomination to the second-place finisher just out of personal preference. They will be under much scrutiny. And blowing up the party to save a nominee will not be undertaken lightly.