Originally posted by Bingowings:

"Another idea that occurred to me was rather than removing Threepio from the prequels perhaps sticking him (the full Gold version) in all of them..."

Hell, it could be pulled off very convincingly if you outsourced it to someone with green-screen experience and got an actor in a decent looking 3PO costume. Plus, since the actor in the suit would be able to make gestures appropriate to the lines, you would have a level of control over the direction of the character and his function in the story that you would not have if you were just redubbing existing 3PO footage with sampled Anthony Daniels dialogue. Adywan has already proven his proficiency with changing backgrounds completely, so this could be very feasible.