Wild guess/proposal for each team's three:
Minn - Wisc, Iowa, Mich
Wisc - Minn, Iowa, Neb
Iowa - Minn, Wisc, Neb
Neb - Iowa, Wisc, Ill
NW - Ill, Ind, Pur
Ill - NW, Pur, Neb
Pur - Ind, Ill, NW
Ind - Pur, NW, Mich St
Mich - Mich St, Ohio St, Minn
Mich St - Mich, Penn St, Ind
Ohio St - Mich, Mary, Rut
Penn St - Mich St, Mary, Rut
Mary - Rut, Penn St, Ohio St
Rut - Mary, Penn St, Ohio St
Could not get the Illibuck Trophy game in there, though I'm not sure Ill fans would prefer that one over Neb. Lot of in's, lot of out's.
Wisc might also prefer to play in Chicago at NW, but who doesn't? Both Indiana schools are huge into Chicago.
If Ill and NW didn't care that much about playing each other yearly, that would open those up.