I tease them and gently tap on the brakes, if they sit on my right shoulder I gently drift right... 99.9% of the time they give up.
I sometimes get close to the car in front if they're going well below the speed limit just to coax them into accelerating, but I never deliberately sit on anyone's tail for extended periods. You've got to be careful because I've heard of people accidently tailgating unmarked police cars and getting arrested.