We do this on the Fords and GMs quite a bit. It's a very simple Two pole switch $2.73 @ radio ShaQ. You interupt the VSS (Vehicle Speed Sensor) or (Velocity Speed Sensor) wire. I'm told from a friend over at Mitra the VSS wire on the 2011/12 GC media center units are Navigation wire colors:
Blue/Pink – VSS (Vehicle Speed Sense)
Green/Violet – Reverse
Lt. Green – Parking Brake
Keep in mind they don't use the same language we use here, 430N, 470, RER, RHR, etc.. and Mitra online isn't listing the 2011/12 yet. So... I've asked him to confirm this 100% for me.
Now, I know there a few CHRYSLER/Jeep folks here, could one of you find a way to confirm the color code internally? If you do I will test it and report back.