My hypothetical situation:
1) Nebraska has to win out (including the Big XII championship game). Doing so, I believe, will make the Huskers jump Wisconsin, Stanford, LSU. LSU may seem like a stretch, but you do really think a non-"division winner" LSU would be ranked above a conference champion Nebraska? I doubt it, but I guess it'd really be up to the voters.
2) South Carolina wins the SEC (with a strong defense performance they could do it). This eliminates Auburn.
3) 2 of the 3 teams have to loose: Oregon, TCU, Boise State. This is a huge longshot, but possible. It also doesn't really have to happen, if the voters would vote Nebraska over some teams who haven't lost, but also haven't beaten anyone impressive, then we could be talking.
So really it's a longshot, but still very possible. I do think, however, as long as we beat A&M and Colorado, if we lose the championship game we could still go to a BCS bowl game, which should be considered a successful season.