Metra is currently working on units that allow you to use factory steering wheel controls. They are brand new and aren't working all that great yet. With the setup they have, you have to mount a "remote eye" somewhere facing the cd player. It is like the little eye on the front of your remote control for your tv, so that when you press the steering wheel buttons, the command is sent to the eye and it shoots the signal to the radio like a remote.
I'd suggest waiting until they improve on them.