love the above idea.....

below would be my idea for throwing the audience off the trail of Anakin=Vader.... probably needs major tweaking but here is my ramble...

starting in Episode II:

Obi and Anakin have formed a great close relationship, but with the recent developments of Dooku going rogue, Obi is assigned a second apprentice that once belonged to Dooku. He gets along with Obi-Wan and his new peer in Anakin, but its clear that he is a bit of a third wheel, he begins to show some jealousy and is constantly trying to outdo Anakin who clearly seems to have a leg up on him in almost all aspects of their training... not to mention Dooku tries to seduce his old apprentice and tries to get him to join him on a few choice encounters.

Anakin meanwhile continues down a very similar path that we currently see.... and then Mustafar happens.... he is confronted 2nd apprentice rather than Obi-Wan... the fight goes down in a very similar fashion and ultimately ends with with anakin arm and legless at the edge of the lava didn't have the high ground, and the 2nd apprentice also states how his skills have grown.... Anakin gives one last giant force push to attack the 2nd apprentice and throw him into a pile of coals before he is consumed by flames..... at this point Obi-wan has arrived on the scene to see the end of the battle, what has become of Anakin says a few words to him, picks up his saber and he also sees the 2nd apprentice badly injured rushing to his rescue....

The next time we see Obi-Wan, the 2nd apprentice is on a respirator slowly recovering... (ultimate vader-fake out) the rest of the movie progresses with obi-wan apprentice-less (maybe he can confront Grevious at this point) and ultimately we would see a suited Vader save the emperor from Mace, raid the jedi temple, etc...