Bingowings said:
The way I would do it is change the reference to getting a new apprentice and merge it with the reference to Lord Vader taking care of the Seperatists from later in the film (Palpatine already knows he is going to call Anakin Vader when he turns and he knows he will succeed).

I'd then hide Vader behind a cowl or mask on the attacks on the Temple and on Mustafar (making a virtue of the previously silly Sith eyes, Vader now has them all the time until Luke saves him, to create the impression this is a new character and Anakin died trying to save Mace Windu).

Removing references to Anakin (in fact most of the Volcanic duel banter) would complete the trick.

The only problems are the lightsabre and the "former pupil of mine".

It might be possible to manipulate events and the picture so Padme is given Anakin's blue sabre as proof of his death and Vader uses a red blade doing his various dirty deeds.

It wouldn't be too much to expect Obi-Wan to have a new Padawan after Anakin is knighted but getting him into a scene would be hard work.

I was wondering if there was some way to change up the timeline (probably not) and have the emperpor mention a new apprentice early in the film, then Obi/Anne fight, then Anakin "dies", THEN have Vader attack the Seperatists. That does create some issues though...example: why would Anakin go to Mustafar in the first place?