Originally Posted by Mason32

He can not.

If he is flying as an SIC and the operators Operations Specifications require an SIC, then he can not by definition be PIC.

There is tremendous case law available on this, and a fairly well documented enforcement action involving a King Air 200 (also certified for single pilot) but the company Ops Specs required two pilots. The FO was logging time as sole manipulator of the controls on the part 91 legs. Some six months after being employed there, a minor gound incident - not with the FO controlling - resulted in the company records being looked at including the logbooks of both pilots. The FO was violated for EACH time he signed his name to a logbook page with PIC time listed for the part 91 King Air legs. His case was appealed tot he full NTSB panel, and the FAA's suspension was upheld.
The entire case, and many others, are available on the AOPA website in their legal case studies section.

Go ahead and log it if you like; but the case law is not on your side.