The seat removal is the same as the sedan. Take a look at the early steps in this post here:
However, if you are routing a cable to the cargo area in back, I would suggest that you take the same route as other wiring, and go under the dash, down along the driver side door sill under the carpet, and up the side bolster of the rear seat into the cubby where the CD changer cable is located. More work, but much cleaner.
You can see how to route a cable in that manner in this tech article:
2002 A6 4.2 Silver/Ebony, Tip, Premium, LOTS of mods!