If he has any sense he will pick someone to help him gain some bonafides with conservatives. He has to know that conservatives don't trust him, and that even though they will probably vote for him just because he's not Obama, they won't be enthusiastic about it. Energizing conservatives would be the smart thing to do.
Of course, let the damn Rovians get involved and he'll be picking Charlie Crist or the recently-become-available Dick Lugar.