Maybe Vicki will be resurrected as a zombie and Stefan will kill her?
But that's still in cop-out territory. All the characters are either non-starters because they'd destroy Stefan's relationship with Elena (Jeremy, Ric, Bonnie, Caroline, and I guess we need to include Damon) or they're who-cares-ish (any of the parental units, Matt, resurrected Vicki or Anna). Who have I forgotten? Oh yeah, Tyler. There's a possibility.
If the writers want to get radical, they could have Stefan kill either Elena or Damon, and then have the season finale cliffhanger hinge on whether and how they are resurrected (because of course they would be resurrected, but in what sort of shape/attitude/personality?)
Damon, yeah, that's the ticket. Stefan should kill Damon!!!
Now I have a reason to watch the whole season.