Mapping Xbox One trigger axes in game

[paralipsis]

I am having difficulty mapping the right and left triggers for the Xbox One controller in the game. Each trigger is recognised as its own axis, so there seems no way to have each mapped to a different direction. Worse still, the zero-point is 50% of trigger depression, so that the trigger at rest applies 100% in a particular direction.

I'm trying to apply the triggers to the roll axis so that the left trigger applies roll left and the right trigger applies roll right, but I'm not having any luck. Applying one trigger to the primary and one to the secondary control of the roll axis doesn't seem to help, nor does any combination of inverting one axis and not the other. Basically, any time I map one of these triggers to an axis it makes any vessel uncontrollable.

I am on Windows 10 x64, using a wired Xbox One controller.