Would it be do-able to try and roto dooku into the Jedi council throughout the film? You would have to find some point where we see dooku sitting down with his whole body visible and idk if there is any point in the films where we see that. If there is though, that would be I think a good enough way to make him not just seem to appear out of thin air.
Maybe in the deleted scene from II? It’s very dark, though, and I imagine it would be terribly difficult to get him into the bright council room.