Hi, just read other post about joysticks. You here talking about joysticks for Elite Dangerous, but my subject is the same for other simulation games. Did you ever modify a controller to suit your needs?
here is the work i did some time ago:

(it is in Portugues, but you can get the point, or translate it in google)

I think i will do it for Elite. I have an old Microsoft sidewinder, that has all axes, including point of view, thurst, and rudder. But extra buttons near the joystick are nice. I think keyboard buttons don't have the feel. Doing personal buttons outside the keyboard makes the experience much better.
Did you ever do it? It's really simple. You just need to grab an old USB keyboard circuit and find out the pinouts, and put wires from it to external buttons.