For about $1500, you can buy an adjustable wing for your trunk. I’m unclear on whether you’d do a 61" or 67" application on a B8. The main idea would be to achieve downforce on the rear end of the Audi, which is a bit light with 58.6% over the nose in my car. I’m assuming that the BMW E90 application would bolt onto our cars nicely at a body shop.
http://aprperformance.com/racing-product/gtc-300-adjustable-wings/
The 67" looks a bit wide.
http://i17.photobucket.com/albums/b79/mlab601/RearWing02.jpg