As with so many things, the answer is in LASORS -
Section A, Appendix B in this case.
There are two cases given where PICUS may be used:
"Co-pilot performing the duties of PIC under supervision of pilot-in-command." You can only be a co-pilot on an aircraft which is certified with a minimum crew of two or more, so this doesn't apply to any single-pilot aircraft, regardless of how many pilots are actually on board, and what type or class ratings they have.
"Pilot undergoing any form of test flight with a JAA or CAA Authorised Examiner (other than [pilot undergoing a flight test in the capacity of co-pilot])" where you can only log PICUS fo a successful test.
So the answer is No. In fact, as BEagle has hinted, you can't log the time at all if you're not licensed to fly the aircraft, unless you're with an appropriately rated instructor.
FFF
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