I believe that you can train in your N reg as long as you are training an FAA student and you are an FAA CFI.
You can also train FAA students in your G reg plane as long as you have JAA CPL and FAA CFI (Grey Area).
I don't understand your problem as there are loads of clubs in Europe that do American Training with N reg planes.
Good luck anyway, I understand the frustration which is why I now instruct in the US.
