Okay, after taking your comments into consideration I came up with the perfect VMA performance.
So Britney comes on stage to perform her new single. She is disguised as an alias-- maybe Amy.

She is wearing the black wig from "Toxic," and she also has the same make up on as she did when she wore the red wig in "Toxic" as well. The audience thinks this is a new artists with a new song and killer dance moves. Towards the middle of the song (or at the end of the song) the dancers slowly take off her disguise one by one to reveal Britney and the crowd is amazed.
Inspiration comes from when "Womanizer" came out. People had no idea it was by Britney at first.