Well, let's not waste time thinking about bringing SW actors to work in a fan edit. They can't do that, even if they wanted.

The best thing you could do is to have someone else to play the character in the movie. I always thought that Obi-Wan and Vader duel in ANH could be highly improved because it isn't hard to find someone to play Vader and Obi-Wan is wearing his hood during the fight (new scenes could even shot obi-wan from behind and /or from angles that you wouldn't see his face). I believe something similar could be achieved with Darth Maul (specially if he is using his hood in the new scenes as well).