a friend of mine wanted to do this with me as well when i was hours building, so i did a bit of info digging to see what people thought of it.
i learnt very quickly that if you are the one that writes your name in the aircrafts documents when you take it out, you and only you are PIC. another person may be manipulating (like when an instructor takes someone up for a trial flight) but you are still in command of that aircraft.
even if your friend is not logging the hours, if the CAA decide to go through your log book with a fine tooth comb, they will go back to aircraft logs and not see your name in them as PIC. when they come back to you its game over as ive been told they will just take you licence away.
dont forget that unless you flying somthing like a jet, all these GA aircrafts are single crew.