DO NOT DO THIS
Although some people on these forums will tell you that you actually should write your PF hours as P1 U/S when flying with a Trainer, this is absolutely not accepted anywhere outside the UK.
I have frequently told people here that P1 U/S should only be used when undergoing Command training, and never otherwise.
You will see strange looks on any EU carriers recruiter when she/he examines your logbook as FO and sees hours logged as Captain of the aircraft, which is the defenition of P1.
By the way, Ii is not recommended to have your logbook with you on the flightdeck.
BRGDS,
Despegue