Unfortunately, you can't use the steering controls. Old BMWs used iBus, which has been "tapped" into, and there are computer hookups to wire into it and use steering controls. There is nothing like that for the newer E9x series, since they use CANBUS.
One option that I thought of is simply rewiring the steering controls to ONLY control the computer. It wouldn't be too hard, since they are just buttons - but you'd lose the radio control functionality, so might not be ideal.
I've given up on the idea - touch screen is fine for me.