Incorrect, you can act as an SIC in any airplane that requires two crew so long as you are rated in category and class. Only case the SIC rating is required is for int'l ops. If I need a copilot in the Sabreliner, I'm perfectly legal to dump my CMEL friend in the right seat.

Insurance SIC doesn't necisairly mean FAA legal SIC. Insurance may just want another pilot sitting in the right seat for redundancy sake. Now in theory they should be qualified in the airplane to make insurance happy...

You're legal to use your friend sonlong as ge meets the remainder of the requirements set forth in 14 CFR 61.55. This includes, among other things, an instrument rating, aircraft familiarity, and three takeoffs and landings as sole manipulator of the controls, crew resource training, inflight maneuvering with an engine out whole performing PIC duties, etc, with ine previous 12 months. Then you can "dump" your friend in the right seat for a trip.

I use the right seat in "my" 350 as paid training time for new turbine candidates. I just sign it all off as dual.