Xbox360 Controller...trigger differentiation?

I was wondering how you can tell which of the two triggers have been pulled and how much. There's only one axis that they are mapped to (both in TorqueScript and in the GameControllers control panel in windows) so there's only one value. One trigger is mapped to the + axis and the other is mapped to the - axis. The trouble is if you pull them both at the same time (and your controller is calibrated) you'll get zero as the values just cancel each other out.

Any ideas?