This kind of thing is talked about every time an incumbent president is running for election.
While kinda fun to talk about, I do not belive it will happen, here is why.
1) Preisdent Obama is not so desperate, the poll numbers do not look so bad. The infighting in the Republican party is giving him hope and the economic numbers keep comming up better and better.
2) President Obama appears to be a very loyal man and VP Biden has not done anything to change the decision Presidnet Obama made when he origionally chose him over Hillary Clinton.
3) President Obama and the Clintons do not appear to be very friendly.
4) While the Republicans have been unusually nice to Hillary Clinton, put her on the ticket and the attacks will begin.
5) All reports are that Secretary of State Clinton does not want the position.
I do agree that if the Preident did this act, if it did not create a feeling that he is desperate, it would help his reelection chances, but the R's would spen it as him being desperate. In the end VP's, even Hillary, do not make much difference in a Presidental race.