I am experiencing the exact problem. For a few brief moments, I had the axes of P2 working, then it was gone. Most interested to hear if you come up with anything. . .I will do likewise.
I should have mentioned that my current path of thinking is that Linux is expecting a USB joystick to have analog axes, GP Wiz does not. So I'm finding a few things about mapping the axes to keypresses. . .but I'm tired and going to bed.