Reading 'not defined' Controller Axis Input?

I am working on a mod for the game Scrolls to make it controllable with a (Xbox 360) Controller.

I can read all the Button inputs plus the default Horizontal / Vertical input axis fine. However I am having trouble reading the other (right) analogue stick and the left/right triggers.

Normally you would just assign the correct joystick axis in the InputManager. However when modding Scrolls you basically just hook into a few of the game's functions. This means you can't edit the InputManager settings as you don't have the actual Unity Project.

Basically I can read the buttons with Input.GetKey and just the Horizontal/Vertical Axis with Input.GetAxis, as those two are predefined by the InputManager by default. However the other Axis are not.

Is there any way to 'directly' read the joystick axis without it having to be defined in the InputManager?