Never mind, I was able to figure it out. For those interested, the trick is to make your X-axis value negative numbers. Then hide the original X-axis value on the Dimensions tab, and create an expression where you wrap the X-axis value is a fabs() function and select "Text on Axis" to display it in place of the original X-axis value. In my case, I found there were too many value displayed, so I added some additional logic to display only a few key values in order to not lose scale.
Edit: I finally got around to documenting specifically how this was done. For those interested, you can read the article here: http://www.infinityinsight.com/blog/?p=246