switching turning direction using arcade drive?

[Kyledoo]

We have implemented a way to change the polarity of the motors by hitting a button(simply using the SetInvertedMotor), and in this way, we can select which end of our robot is the front. However, while in the reversed mode, pushing the stick to the left turns the robot to the right. I was exploring a way to basically invert the x axis of the joystick. any ideas on how to do this? oh and we have our first matches tomorrow, so i'm hoping to figure it out sooner rather than later!
We are using C++