I have no experience modifying USB sticks to work with gameport ones, but I did play around with modifying the white KoP sticks in an attempt to make something useful out of them, and the results was this joystick:
http://www.chiefdelphi.com/forums/sh...ad.php?t=62582
If you don't need the buttons, it is a great mod. It drastically improves the white joysticks' feel and centering. I personally like joysticks with very strong springs, so the spring mod may be a bit much for some, but just getting rid of that massive handle makes the joysticks vastly better.