I had a look ad the Joy2Key software but it doesn’t look like it can help in this case.
QGC does not support keyboard strokes in lieu of joystick buttons unless I am missing something.
Joy2Key can change the mapping of the buttons to be triggered by another but you can’t assign more than one trigger per button. (IE button 16 is my “shift” key and I want it triggered if buttons 17 or 18 or … 32 is pressed)
Did you figure out a way that escapes me somehow?