You can get away with this.
What you are selling is club membership, not aeroplane rides. The rides are said to be inconsequential and your fee covers membership of, say, the Jet Provost club. The pilot need not hold a commercial licence, since he is not flying for remuneration.
Not sure of the exact details, but be assured that this can be done legally, though just barely....it's happening now and the CAA has been unable to prevent it.
I suppose that, if an accident were to occur, the "student" would have to sue the pilot or owner for compensation. Since the "student" was accepting a freebie flight, it may be difficult to make a good case.
I don't think that this has been tested in court. You could be the first !