A solution I did was a bit tricky. I wanted to be able to have the functions when I drove, but not when other people drove my car, I wanted them to have to put the parking break on. So I installed a simple switch, that when on grounded the system, providing the funtion, but on the off side of the switch I had two wires, the one from the stereo, and the one to the parking break. This way if the switch was off, you could ground the system by pulling the parking break and work on the system, and if the switch was on, it would always work. The switch is installed in the glove box and I leave it on all the time, except when someone else is going to use my car, then I flip the (somewhat) hidden switch, and then if they want to use the functions that require it, they put the parking break on.
Also this might be good if you get pulled over, flip the switch and if they wanted to test the system they would see you needed the parking break on, and that you "didn't" bypass the system. Hopefully this might help at least one person....