This is just a demo of a mod I made to my Saitek joystick to allow me to connect an external variable resistor (pot) that is built into my homebrew rudder pedals.
I added an 1/8" stereo headphone jack to the joystick such that with nothing plugged into it, the joysticks internal "twist axis" pot is connected as it was originally. Plug in your external pot and that axis is now driven by whatever the hell external device you dreamed up.
Ill add a link here later with detailed instructions for performing the modification.