Yes you can with a program like GlovePIE BUT Turbine is checking with legal because they are checking if alternate input devices will be against their TOS. This mostly comes under things like the G15 keyboard which can record macros. Turbines TOS states that no macros or 3rd party software can interact with thier .exe. We are anxiously awaiting an answer on this because it could affect many people.
Cool, yeah I don't want to macro, but I've been playing piano for about 30 years and it would be nice to be able to use my real-worldly talents in-game. Although I could always remap the keys on the keyboard to be similar, there's still that problem I had playing chords. I just want to be able to play proper chords, not just melody. Thanks for the speedy response!