I don't see anything wrong with logging pass time, especially if it is something out of the ordinary to you. If your log book has an any other flight column it can be used for that purpose.
What do you log if you are with another PPL and you fly outbound and they fly the return leg?
Or do you assume you stayed where you went?
In such a case I always recorded the non flying leg as pass. It completes the picture, and you are usually doing something even if its just keeping an eye on the flight.