Hi Nick,
Nice car. No I lost the will to live and gave up. Got a different seat with the spindly leg
at the front which I'm not convinced would be as good as a top tether.
Fitted 2 genuine Audi isofix bars myself not cheap.
The images above show a part number can't guarantee it. But I think you could only fit one top tether seat
as the recess is only on RHS of the back of the seat.
Seems to me that the Americans had a solution but was unable to find out.
Good luck. Let us know.
Steve