It helps that I'm really tall, but it's worth it for the look on their face when it turns from 'bored paternalism' to 'we might have to watch what's going on here'; it takes some of the initiative from them. It's a subtle way to change the power dynamic, especially if you're tall - you can no longer be talked down to, plus you're free to move. Being free to move isn't about posing a physical threat, but being able to control your end of the conversation better, plus you can watch what they're doing. Of course you should always, always remain polite, but screw being in the entirely submissive position of being locked into your seat.
Incidentally, the 'random' checks have stopped in the past 5 years that I've had a newer car... and curiously my mother has never been 'randomly' stopped.