Peter as Sylar
could work. He could initially have started out as good old Peter Petrelli, then in the future something happens which causes him to turn bad ............ mind control, loss of faith, who knows.
Perhaps that's why Sylar is taking the brains of all the people with powers - if he is Peter (and his own power is to absorb others) then perhaps having parts of those brains around him at all times enables him to maintain his powers. Thats assuming that they have discovered there is a certain part of the brain which controls the powers of all heroes.
Long shot, I know
Gaz