SITL w/Taranis more than 8 axes

I’ve set up SITL on Ubuntu with my Taranis X9D+ as controller. It’s all working, except for one thing. I have a Taranis three position switch configured on RC channel 9, but the joystick driver seems to have a fixed idea that the Taranis is 8 axes and 24 buttons. This means RC9 is seen as a button with only two states which doesn’t work for a three position switch. I can’t see anywhere to change this - I’ve tried jstest-gtk and jscal. Any pointers would be greatly appreciated. Thank you.