http://www.ross-tech.com/vag-com/cars/absbleeding.html
That link explains the procedure. You trigger the system via the vag-com, press and hold the brake pedal when prompted, it will go to the floor and cycle the abs pump. You have to hold it firmly as it will force the pedal back up. Takes about 5-10 minutes.
Some cars can be done without the vag-com, I found short cuts on a few different forums but none of them applied to my VW, not sure about the earlier Audi's.