^Couldn't Beatty just be an executive producer on a film made by someone else? That's how it's often done where film rights are concerned. For instance, every Batman movie in the past quarter-century, not just the live-action Burton, Schumacher, and Nolan films but every animated theatrical or direct-to-DVD movie that's been made from Mask of the Phantasm
through the upcoming Dark Knight Returns
adaptation, credits Benjamin Melniker and Michael Uslan as executive producers, not because they're the ones making the movies, but simply because they're the ones who own the motion picture rights to Batman, so anyone else who wants to make a Batman movie has to do it with their permission and cooperation.