Just keep your change in your pocket, or the center console.
If you put it in the tray, you're going to have a bunch of change falling in behind there.

Then you'll be trying to figure out why your car is making strange noises from time to time.

 

http://www.audiworld.com/tech/int7.shtml

might want to try that, next time im at the dealership im prob gonna pick one up. doesnt say it doesnt work for b6's. dont know if your armrest is the same size though