Call me crazy, but with the numerous plugins that enable Twitter crossposting, I have to think this could be accomplished within the postform on P2 or Prologue. This would be excellent for multi-author blogs, for instance, and those not wanting users in the admin panel which is one of the true benefits of P2/Prologue.
The Commentwitter plugin uses ajax to neatly tuck a Twitter username/password form into the comment post form to make this happen.
I have to think if this can be done with a comment form, it must be possible with the P2 or Prologue postform, no? Appreciate any input on this idea.