The fireware level code currently supports 3 main buttons (Left, Right, Middle) 2 mousewheels (Y scroll and X scroll, both treated as 2 buttons each), 2 extra buttons (X1, and X2), and of course the mouse cursor position (X and Y)
These are, or were at the time, all of the mouse controls that SDL supports. So anything more than this would need another hardware lib to access. In all likelyhood, the Razer's software already has its own re-mapping capabilities, so it might be possible to map those extra buttons to a Joystick controller.
I thought at one point I had a test build which mapped the mouse buttons to joystick buttons (mousewheels included), but I'm not sure what had happened to it.