Many operators operate types that can be flown Single Pilot as Multi Crew (AW139, S76, EC155, AS365 etc).
I know of many people who have successfully argued this point to the CAA on the basis of being able to substantiate that the aircraft in question was operated Multi Pilot when they flew the hours on it. Such supporting evidence would include an Ops Manual which specified multi pilot procedures, a letter from the Chief Pilot confirming that hours were flown multi pilot, existence of a structure that had obvious co-pilots logging P2 hours (rather than everyone being a captain).
Armed with most or all of the above (and all the other requirements) you should be able to argue your case with CAA. Like i said, i know many who have. Be prepared to prove it though, and don't expect to swing it just because you've got a few hours on a single pilot type with another pilot sitting beside you - they will want to see that it is genuine MCC stuff. Expect your submissions to be scrutinised!
Best of luck
OH