It's just my opinion but to be honest, and no matter how honourable your intentions, I'd steer well clear of it. It's exactly the sort of thing that can come back and bite you on the bum either in the form of a ‘little chat’ with the CAA or an ambulance-chasing lawyer in the unlikely event of a prang! Crazy, I know but sadly it’s the world we live in.
Better, perhaps to make it an ‘official charity flight’
(see here) at least, then you’re covered from any trouble from the CAA if not from the damn lawyers!
BH