We had a debate about this in our group recently. Suppose a PPL offers and pays for a free flight in a Permit aircraft as a donation to a respected charity auction. Would this flight be any different to any other legal passenger flight which is at no cost to the passenger?
As far as I can see, the only area which might be a bit dubious is that the auction might be construed as advertising the flight.
The document specifically excludes Permit aircraft and the maintenance requirements tend to go against the way Permit aircraft are maintained but I suppose you could contact the CAA to see if they would exempt the flight.
Permit aircraft are used is a lot of YA flying so they must be able to do it. Perhaps it is worth checking with the LAA as well as they have their own way of dealing with things