I do have some experience with this, as I've had a similar problem. What helped for me, was to increase the deadzone of the "C" - stick. I would do so on the joystick as well. About 25 hit the sweet spot for me. Remember, the 360 joysticks are way more sensitive than the GC ones. I bought a converter, to use my GC controller with Dolphin, and I didn't have to do any adjustments to the deadzone.
EDIT: Off-topic, but I had to register just now, to post this response. The reason I bring that up, is because I was already a member here, I am 10000% sure of that. With the same email. What happened?!
EDIT: Off-topic, but I had to register just now, to post this response. The reason I bring that up, is because I was already a member here, I am 10000% sure of that. With the same email. What happened?!