If you are licensed, rated and current for the type of heli then you are PIC so long as it is known/agreed that you are in command of the aircraft. Example, you take along an instructor for a first run of the London heliroutes as a checkout for renting their machines.
If this PIC designation query is for some sort of CAA paperwork, you’re probably going to have to argue with them anyhow. Even if you
- cut/paste the regs into all correspondence
- document the person/date/time of every phone call with them
Regarding the seating location comments above, I’ve never read any FAA or JAA docs which noted/commented where your ass touches the helicopter – just whether you are “in command” of the aircraft.