How do I hook up a SNES controller to a Game Boy Advance SP?

I would really like to build this https://www.instructables.com/id/Adventure-Times-BMO-Roommate-GBC-Mod/ but with a SNES controller instead of the joystick controller so I can still play games that require front bumper buttons. The problem is, I have a minimum of knowledge of advanced electronics, and any online information I could find about what the various pins in the controller plug do is just so much Greek to me.

If anyone could detail to me exactly what wires I'll get at the end of the SNES controller and what they do before I start taking it apart and find they all look the same I would really appreciate it!

Thanks!