Is it not horses for courses?
Departing North Weald it would seem silly to have QFE set - that is bound to lead to a CAS infringement.
Departing Headcorn if you infringe CAS vertically setting QFE instead of QNH is hardly likely to be the cause.
And in any case correct use of the altimeter forms part of the skill test. So any PPL skill test candidate should be perfectly capable of talking to a military airfield - setting the QFE, reporting their height, and then crossing the MATZ at that height, and once clear setting the appropriate QNH/RPS and flying that altitude etc.
Altimeter setting procedures aint rocket science. If people aren't capable of taking one hand of the control column and twiddling the pressure setting dial without it leading to loss of control or mental overload they shouldn't be flying anyways.