Haven't actually seen the opportunity to do this yet... have waved at plenty of other minis but nothing doing. What I do instead is park next to much larger cars for amusement...
I did park my ST between a Zetec and another Fiesta once, all 3 red. I wish I had taken a photo, but my misses was already berating me for parking between them and smiling like a loon. She just doesn't understand!