Is Clinton likely to do this? Of course not. One cannot begin to count the ways in which it might backfire on both her and her party. Nor do I have any idea about the probability that such a maneuver would succeed. But it does theoretically give her some leverage; the threat of being able to do something like this might be more potent than the reality. And it's one reason why going into the convention with say 48 percent of the delegates -- in which case she'd only need a trivial number of delegates to "split their ticket" in order to get the VP nod -- might make a tangible difference for her versus going into the convention with 42 percent of the delegates.
Rasmussen also polled voters in different parties about whether they thought having Clinton in the VP position would help or hurt Obama, and those results are as follows:
Party Help Hurt No Effect* To see him make the point himself, click on the video link entitled 'the VP Spot Belongs to Hillary Clinton if she wants it' in his daily tracking poll write-up.
Democrat 52 21 27
Independent 32 39 29
Republican 18 57 25
Overall 36 37 19