To be honest i still think it comes down to the cop himself.
Everytime ive been pulled over i'm nice. I know that i haven't done anything wrong (i've never been done for speeding etc) and i know they are there to look over the car.
But there are some cops, either who have had a bad night/day, or are just out to get you, and no amount of nice-ness can change their decision.
I find at RBT stations, unless they are busy, you can get off without opening your bonnet. If they are quiet, get ready to "just drive up over here sir" and starting opening your bonnet.