The sticks are just voltage dividers.
You'd need to sever the center Stick line and get a Microcontroller and DAC between them. Stick line to ADC of the micro then micro to DAC to controller. Then you can read the Stick value and code the micro to do whatever and output it to the DAC for the controller to read.
https://www.acidmods.com/RDC/XB1/X1-SCproto.jpg