The last two companys I have worked for who ran single crew ops and multi crew it has been an unwritten rule that its called single ops for a reason. Even if there is a fully qualified pilot sitting in the RHS seat it is still run by the LHS as single crew.
They may off load by asking said person to get ATIS, contact company or fly it for a bit while they sort the NAV out or plates. But during taxi, TO, climb, approach,land and after landing. It is all done single crew with no input from RHS.
Experience has shown that if you knock the pilot out of his flow for the flight there is a decrease in the safety of the flight.
Unless you have a set of SOP's designed for multi crew and the crew is trained in using them you are setting yourself up for potential problems.