They need Washington State to upset Washington to and win the Pac-12. Even better if they do it with 3 losses. The Big 12 champion needs 2 or more losses. Could also work with a 2+ loss team winning the Big 10 or ACC, but this seems the most likely path.
At that point, it would be undefeated/1-loss SEC, ACC, and Big 10 champions all in, and then down to Texas A&M, Washington, and Louisville (all 1-loss teams who didn't win their division) for the 4th spot. Maybe Louisville needs to pick up another loss along the way too.