Yes, and as PIC. FARs 61.51(e)(1)(i) applies: [ QUOTE ]
(e) Logging pilot-in-command flight time.
(1) A recreational, private, or commercial pilot may log pilot-in- command time only for that flight time during which that person—
(i) Is the sole manipulator of the controls of an aircraft for which the pilot is rated;
(ii) Is the sole occupant of the aircraft; or
(iii) Except for a recreational pilot, is acting as pilot in command of an aircraft on which more than one pilot is required under the type certification of the aircraft or the regulations under which the flight is conducted.
[/ QUOTE ]
You're correct that you are not the acting PIC without the endorsement, but you can still log PIC time as the sole manipulator of the controls. Also, I assume you are appropriately rated. "Rated" means category and class (airplane single-engine land, for example).