What a lot of nonsense some people write.
Yes, but I think it could be you, IO540. Apart from you there seems to be a concensus here. Maybe you skim read the previous posts but I'll break it down for you:
AlexKA
am I allowed to log this flight as co-pilot (P2)?
Flying Farmer
To log P2 time you must be operating a multi crew aircraft recognised by your authority
Agreed, you can write whatever the hell you like in your own logbook and of course, if he's that way inclined, the original poster can log these trips in the 'other' column as pax flying as long as he doesn't try to include the hours in his total time.
It will be an illegal entry if you log it as "PIC" or "P1".
And it will be an illegal entry if he logs it as P2.