I really love making these of projects, from analog to digital and digital to analog hehe, there`s an easy way to use a joy stick without hacking on the board itself sir, it`s a software based control which I used almost everyday to zero on materials I cut, keyboard to joystick mapper, then you can map the 12 buttons there according to your preferences, you can even create a macro keyboard combination to control some specific buttons on MACH3
Once you configure it you dont need a keyboard anymore, just autostart the mapper software everytime the PC starts.