Start with an Audi:
There is one hex screw that attaches the rear wheel well to the rear bumper. Remove the one screw
from each side:
Remove trunk liner to access the bumper bolts
Make sure an exit tube behind the passenger rear wheel well is not tangled
With the 2 hex screws and 4 bolts removed, you can push the whole bumper forward
With the bumper pushed forward (as far as it will go), you will now need to unclip the bumper from the side supports.
Go to one side, grab behind the bumper @4" down from its top and pull (gently but firmly) straight out / a little down (towards you) from the side of the car. This will release the top portion of the bumper.
Look down and you'll be able to see the bottom clip still attached, just give that a little pull up / out to release it completely.
Do the other side.
What the attaching clips looks like from the inside of the removed bumper
With your bumper removed, you can clear out the sunroof drains, one on each side. Make sure your sunroof is open before proceeding.
Use a standard speedometer cable and snake it through starting at the exit point (under the rear bumper) which will lead thru the rear of your open sunroof.
Do both sides.
To reassemble your bumper.
Pickup the bumper and slide the bumper supports (on the bumper) into the bumper holes on the frame of your car. Slide the bumper as far forward as it will go.
Ensure the bumper lines up correctly with the rear wheel well.
Once it is lined up, push each side of the bumper straight into the side of the car to reattach the side clips. They should 'pop' back in.
Once secure, pull the bumper back (rearward) to line up with the 4 bolt holes in the trunk.
Insert and secure each bolt (good and tight). Make sure you reattach the cargo net plate and hook as you insert each bolt.
Screw in each hex screw on both sides of the rear wheel well.