Guys, in P500, not only you are getting more power but the acceleration response changes as well. Think of it like a mod with 100+hp gain with an ecu tune. Please try a search in the forum as I remembered reading a more detail description on the matter.
even if you could start your car is p500, is it p500 or p500 sport? i think just pressing the power button only gives u p500 and not sport throttle response. and u still wont have mdm without hitting the m button and to me, the car is useless without mdm or traction off completely cuz the traction control kicks in way too ofter. for me the most annoying lack of feature is that you cant program the active seats into your seat memory. u have to either press it 3 times every time or thru the m button.
I had the ECU tune which defaults the M button to P500, S6 and DSC off. If it is wet, then I can just manually turn DSC back on. Didn't know you can program it to start with P500. Though since it is just programming, anything should be possible. I can't stand driving in P400 and S3 at all, unless in heavy traffic.