The RS6 tow hole is behind the passenger intercooler grill, so you'd have to remove the grill or punch a hole through it (don't do that please). In either case, you would be blocking airflow to the intercooler, and that's not a good idea.

Most RS6's should have the front plate adapter already installed. If you happen to find a car that never had it installed, and you really don't want to punch holes, then use the magnetic options described above.

Personally I don't think the RS6 looks too bad with a front plate. The bumper was designed to have a plate (albeit the Euro style), so it doesn't really mess up the front lines too bad.