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.
I think you will find that most group paperwork are unofficial documents and aircraft logbooks do not have pilots names entered, in fact there is no reason this group member could not go to his group and see if he can get them to endorse him allowing him to let Weeman fly it as he does - but HE would be the aircraft commander not the group member - indeed, there are some groups that actually have non pilot members who can fly in the aircraft with (group approved) non group pilots.