The FAA examiner does not have to be the PIC; they can do the checkride from the back with the instructor and the candidate in the front seats.
As I understand it (but bookworm and 2Ds will know for sure) you can exercise your IMC rating in a G reg aircraft.
There are a number of outfits who can provide FAA IR training in a G reg, ACS at Enstone is one such establishment. It requires the instructor to have both a JAR and FAA (C)FI(I) ticket.
I think that if you have an IMC you can fly with anyone in the RHS be it your next door neighbour or an FAA instructor. However if money is to change hands that will obviously put a completely different slant on the matter.
FAA examiners do come to the UK apart from the establishments mentioned there is Tom Hughston in Norwich who does exclusively FAA training
www.flyafts.co.uk
HTH
FD