Bringing together these posts:
If the operation requires 2 pilots in the Ops Manual then you must be type rated on the aircraft to sit in either seat. If you're being offered a seat without a type rating then, by definition, you're not required to be in the seat by the Ops Manual and so you can't log the flying.
Speaking JAA, the PC-12, being a High Performance Aircraft, requires that you have exam passes at ATP level (or an equivalent approved course) before you can get a rating on the aircraft.