According to the local CAA here in Iceland, if the aircraft is classed as a single pilot a/c but the type of flight conducted requires two pilots (e.g. commercial ifr/night flying) it is possible to log the flight either as PIC or SIC, but not Multi-Crew.
Aircraft such as the Do228, DHC-6, Fairchild Metro and the BE-20 which are flown single pilot in many parts of the world are always crewed by two pilots here, and these hours are logged as multi crew since the pilot's type rating stipulates two flight crew members.