Whe I started out flying Kingairs for a 135, (single pilot certified, SIC required for insurance), I sat in the right seat, but didnt have a 135 SIC checkout. I logged the 135 flight time as "total time" but didnt log it as pic or sic. When I flew the 91 legs I logged it as PIC as I was properly rated and trained for the airplane. This was the reccomondation of the cheif pilot and local FSDO. I know this is a grey area, but I have been on many interviews and it never once came up as a problem. I think that is the best way to log it.