As Pomme said there was a guy in the US put a tow bar point behind his number plate, it was to tow his go kart so fairly light trailer weight. The R is not designed to have a tow bar.
But if your just after a rear towing point for getting you out of the sh#t. I fabricated one that i use for track days incase you get stuck head first into the kitty litter and the unforgiving marshals turn up to pull you out.
Its not the best, but it is better than nothing. Can only be used while pulling perpendicular to the car NO SIDE loading.
Fabricated out of plate steel which fixes to both side of the rear rightside chassis rail above the right exhaust tip. There is 3 or 4 captive nuts up there in the chassis rail.
I am in China at the moment so cant get you any good pics on how to fix but found this to point you in the right direction if thats what your after.
Many thanks for the input.... I should have been more clear, the towhook is not for use as a "trailer hitch" but more for use as an extractor hook-up point should I do something foolish....its the old boy scout thing.
When I bought my R32 mine was fitted with a towhook aswell. I made a deal with the dealer that they could keep that tow hook if they supplied me with a new painted rear bumper. But during the test drive I made a picture of how the rear bumper looked to make place for that tow hook.