The long shaft ones are fine for undermounting without routing out a pocket for the stick.
If you want a clean undermount using a short shaft and a routed pocket, check out EMDB's shallow undermount method
here.
Route a pocket on the bottom of the CP the size of the joystick mount plate.

Add support blocks.

Make a metal support plate to hold up the joystick and support blocks.
Instead of a square plate, you could just use 2 pieces of flat bar-stock to hold the support blocks and joystick in place.
Secure the metal support plate to the underside of the CP using 4 threaded inserts. (he went a little overboard

)

Scott