I don't love giving cheer ideas, mostly because they tend to sound stupid when you type them out. But if you look out on the web, there is some material to work with. I'm sure a clever American student can come up with some decent cheers/signs from it:
Gleaned from the Colgate website... I see that they have two of three triplets on their squad, Kyle and Kendall Chones. The third triplet, Kameron (good name, poor spelling) attends Brown. They also have a sister Kareeda who works for the Milwaukee Bucks and a sister Kaayla (formerly of NC State) who plays in the WNBA for the Mystics (or did... she doesn't seem to be on the current roster). If she is still with the Mystics, I'd suspect she'd be there to watch her brothers play at American.
Their best player is a guy named Jon Simon who appears to be a definite "Opie."
According to this article from the Colgate student paper, the Raiders' last loss to American was "one of Colgate's most devastating losses in team history." Kyle Chones fouled American's Arvydas Eitutavicius with .2 seconds left, and he sank both free throws to send the game into overtime for an American win. In that game, Eitutavicius and Linus Lekavicius combined for 25 points. "Our Lithuanians own you" on a sign?
Hope this helps your nephew come up with some good ideas!