Map + and - input axis values to different output axes

[TRPB]

I'm trying to play GTA Vice City Definitive edition (I know 😂 ), the PC controls for flying are basically broken by design but an xbox controller works. I don't have or want an xbox controller but I do have a joystick.

The problem is, that the Ascend/Descend controls are two different axis on the controler (trigger left/trigger right).

I'd like to map the joystick's throttle control which goes from -32768 to +32768 so that positive values map onto a gamepad's RZ and negative values map onto the RY axis (or any two axis),

(I can then use xboxdrv to map to virtural controller to the xbox controller used in game which is a bit of a pain but works)

Is there any way to do this? It works fine with buttons, positive values can map onto one key where negatives map onto a different key but it doesn't seem possible with axis.