I don't think there should be an EU President, at any point. I don't think Lisbon has democratic legitimacy - British voters had legitimate expectations of a referendum (2005 manifesto - all parties) and didn't get one - and Ireland had to vote twice.
But if we are resigned, the last person it should go to is Blair. He jumped before the electorate got rid of him here (the Commission is the place for failed politicians, so it's a surprise he isn't there yet), and practically sold us out to the EU - rebate gone, opt-outs gone, British interests not defended. Would he defend British interests as EU President? Or more to the point, would he be allowed to defend British interests as EU President? Would his oath forbid it? Would, by having a British EU President (who none of us want in the first place) we be forced into "full" membership - the Euro, Schengen, etc?
And to get rid of a discredited Labour government, only for the new supreme president to be the former leader of this discredited government, would just irritate the voters.
Let him speak to the few who want to hear him - and leave him well away from a post no one wants him in (and no one wants the post!)