JAR-FCL 1 seems to be pretty clear (after more than one reading!) that you cannot log a flight such as a cross-channel checkout as PICUS (P1S) because you are not multi-crew and not flying for a rating or type/class checkout, neither can you log PUT as there is no such examiner qualification for channel checkouts. That leaves only two possibilities: P1 or unloggable. Unloggable is untennable so it is probabaly appropriate to insist that you claim the P1 time.