RodgerF is quite right; Pu/t is your only option. However, FFF said
so it doesn't explicitly preclude you from logging other time as P1US
I wish these things were clearer. Ignoring multi-crew time, the "logging of flight time" bit in LASORS only allows you to log PIC U/S when you do a successful flight test with an authorized examiner. That implicitly stops you from ever logging PIC U/S with a plain-vanilla instructor (for example, a club checkout flight). If you're with an examiner, they should know if it's a flight test or not..
I agree that there are situations in which PIC U/S makes sense - the club checkout is one, but when would an instructor ever settle for SNY when they could have P1?
I bet there would always be a reason to take control. At the end of the day I believe that the CAA count PIC U/S as P U/T for the purposes of licence issue, so I guess we shouldn't care