Copy the following files to this folder: HID.cpp and USBAPI.h
C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\HID.cpp C:\Program Files (x86)\Arduino\hardware\arduino\cores\arduino\USBAPI.h
Download the HID Descripter tool here: http://www.usb.org/developers/hidpage/dt2_4.zip
Other references: http://helmpcb.com/electronics/usb-joystick http://helmpcb.com/electronics/modifying-the-joystick-hid-descriptor http://www.imaginaryindustries.com/blog/?p=80