I'm not sure why you want it to think its a keyboard, but that doesn't sound entirely necessary to me for what you're doing. If it is in fact necessary, ignore my response.
Theres this thing you got in your kit of parts this year called the TI launchpad, its in a little red box. Once you choose a firmware model for it, you can wire your buttons up to it, and it'll act like any other joystick or controller you would plug into your driver station. We haven't got our operator console up and running yet, but we've done some preliminary tests and the thing works great. Its really easy to wire and is recognized by the driver station like any other controller. We haven't tried programming for it yet, but as it behaves just like a Joystick, I'm almost certain it will be easy. Make sure you use 3.3v for all input devices(switches, buttons, pots) or the board makes smoke and you blow out a channel.
http://processors.wiki.ti.com/index....cs_Competition