Maxclimb, I agree with the guys. I can't see any way you can log it. I think the CAA may have misunderstood what you were asking, or you may have misunderstood their answer.
If the aircraft is S/Crew, operating on an AOC, you can't log it because you're not Base/Line checked, therefore not the commander, therefore not a required member of the crew.
If it's M/Crew there will already be two drivers and you can't sit in the seat and log it.
And if it's a Safety Pilot operation, then you are still not a required member of the crew, and CAN log non-required and non-AOC positioning flights if you fly them and can do so on a class rating. But how many of them are there likely to be? Remember that almost all positioning for a commercial flight is considered in itself to be a commercial flight.
Your best bet is to nip over to the USA for a couple of weeks and do some night flying there on the cheap.