I'm sorry to be the be the one to break the bad news, but you won't get the parking sensors displaying on your RCD310 easily. The factory fitted sensors do work with the stereo's but unfortunately the dealer fitted ones do not; it has something to do with the controller they install at the factory being different to the dealer fitted one.

If you find out that I am wrong, let me know what you did pass on the info because I have been trying to get this working for ages. Unfortunately the cost of the new controller and installl aren't worth it ($800); if you go that far you may as well get the RNS510 with a reversing camera.