I recently got and set up xPadder to work with Lemmix (since it doesn't have native controller support). It's not as convenient as playing with a keyboard and mouse, but the setup I have works suprisingly well, and since I use a laptop, it's a bit preferable to trying to use keyboard/mouse when I hook the computer up to the TV.
My gamepad is a 3rd-party Xbox 360 controller, and my setup is:
Move cursor: Either stick
Left click: Click the left stick or "A"
Right click: Click the right stick or "X"
Pause: Start
Fast Forward: "B"
And I also have shortcut key combinations for each skill - left/right shoulder button + X/Y/B/A. Each combination corresponds to the same order as they're on the toolbar (eg: left + X = climber, left + Y = floater, etc). Of course, I have a (rather obscure) combination corresponding to the skip level button - Back + click the left stick. =P