I think OSU would have the best chance out of anyone to get in without winning the conference. Of course things would have to fall just right.
We'll have already beaten whoever Michigan plays in the BIG Championship (Wisc or Neb), and if Oklahoma runs the Big 12 we'll have a victory over another conference champion, who also wouldn't have played in a conference championship game. So I don't see how Oklahoma would jump us.
Then if Clemson or Washington were to lose in their conference championship, I think our resume would be comparable if not better than everyone else being considered for that final spot.