I posted this on the basketball board...
Missouri won't happen due to their rivalry with Kansas. Realistically, the only midwestern programs who might fit the bill are Iowa State, Notre Dame, and Nebraska (because they don't have any natural rivals in the Big 12 that would be broken up). I wouldn't have said Nebraska when the Big 8 was still the Big 8, but the Big 12 has changed the dynamic.
I also could see Syracuse, Rutgers, or Pitt, but both Rutgers and Syracuse do seem a bit east coast. Although, they touch Pennsylvania and isn't that a requirement? To touch a current Big Ten state?
Unfortunately Iowa State doesn't have very good athletic programs, because in my semi-OCD mind, they would be the tidiest answer.
My order of preferences:
1) Notre Dame
2) Pitt
3) Iowa State
4) Nebraska
5) Syracuse
6) Rutgers
Another thing to consider is that we are the western-most team in the Big Ten. It is only natural that we would want to yank a team from the Big 12 because in our minds, that is "closer" the the heart of the Big Ten. But I really don't think Ohio State or Penn State would view it that way.