Let’s say a PT editor felt that the addition of a minor character or two might provide some cover for the shortcomings found throughout the PT. Would it be possible to “bluescreen and composite” new footage to add into any of the movies?

I’m guessing there are enough vocal cues by Liam Neeson, Ewan McGregor, Natalie Portman et al. (between the PT and their other movies) to provide a sort of interaction with the new characters.

Again, I know I’m way out of my depth on the topic of film editing and this idea is likely totally ludicrous. If it’s not, can this be done effectively at all?