How to bind "take screenshot" to hardware button?

I have a Xencelabs device that attaches by USB to my Mac and lets me bind applications and key presses to its hardware buttons. I want one of the buttons to take a screenshot. But when I press the key combo that takes a screenshot, I get the screenshot and the device never sees the button press (looks like the OS pre-empts it because it's defined in the System Preferences). Is there an application I can make or download that would just be an app (not sitting in Menubar or Dock) that I can bind to the button, instead of using the built-in keyboard combo?