I was thinking more of Vader being Anakin's Tyler Durden.

There's a mysterious dark warrior going around killing Jedi and bumping off Separatists and only when Anakin assists in killing Mace does he realise he is the mystery guy.

Some of the things attributed to Grievous could actually be Anakin.

Some of the things obviously done by Vader in ROTS could be obscured and happen before Anakin's actual fall.

Palpatine is fully aware what is going on so references to Vader could be moved to earlier in the film.