Before the Arduino Leonardo (and Leostick) were introduced to the world of Arduino - it was still possible to emulate USB devices with the Arduino Uno using some clever work-arounds, and this has been demonstrated by github user Grouflon.
You need to replace the firmware on the microcontroller, however an experienced Arduino enthusiast shouldn't have any problem with this. Then the keypad can emulate USB keyboard buttons with each of the controls, leaving it ready for gaming or other control purposes.
For the sketch, .hex files and more notes visit the project github page. And for more, we're on facebook, Google+, and twitter - so follow us for news and product updates as well.
If you need to add external hardware or devices to your next Arduino project, you'll need a protoshield to mount the external circuitry. In doing so, consider our range of ProtoShields. From the tiny LeoStick to the Mega.