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I think I see what you're saying -- it sounds like we want the same thing, but I think I have a way to get there with Maul working with Gunray and leaving Sidious a mystery.
It all comes down to the scene where (in the current version) Sidious introduces Maul. Notice -- Sidious and Maul are both wearing cloaks. So we can do shot/reverse shot with Maul and Gunray using the close ups of Maul and the reverse shots of Sidious to double as the back of Maul's head.
The dialogue will be to the effect of "We need help, let's bring in Grievous. Sidious promises he's good." They dial up Grievous/Maul: "Grievous -- go get Amidala. I need to torture her until she signs my treaty."
Set up enough of a Gunray/Maul/Sidious relationship to keep the action clear, but leave room for Sidious to step in later. By the end of the movie, when Yoda and Mace wonder if they met the Sith master or apprentice, audiences will know that somewhere out there a Sith named Sidious awaits... Then we pan over to Palpatine. This is kind of like how Tarkin mentions the Emperor in ANH -- it just sort of flies past until you think about it later.
That will get us both what we want, I think. Thoughts?