LeCuvier
Your axis addition works perfectly on my WH throttle. I used the same zoom axis as you did, but I added the joystick lever as a modifier so unmodified, the axis zooms and modified, the axis controls the HMD. Neat.
PS: I tried your key commands, but while I can see the commands listed in the instrument panel, after assigning keys to them, I could NOT enter a joystick button.