Here's a far fetched one, brought about by my wild associations.
Nuts/geek: In the movie Rain Man, Charlie first thinks Raymond is just nuts. His obsession with certain things is an extreme version of being geek.
Switch: Well, Charlie's view of Raymond switches, and Raymond also undergoes change and has a real taste of the world outside the institution where he lives.
The last hint: Well, they're brothers, duh.
So, Rain Man --> Rainmaker.
I'll get my coat.