I like the EMAW idea of having a separate column.
The PIC signs for the aircraft, has operational control, is the in flight security coordinator, is the person legally in charge of the aircraft, and is the person who has been designated to act as PIC by the air carrier.
If you are listed as the SIC on the trip sheet or dispatch release then you are not the person mentioned above and have no business claiming that you are in your log book.
Now, if the company was to take the time to list the guy as PIC on the non revenue / part 91 legs then that's a different story, but I've yet to see that happen at any company that I've worked for.