....but the giving of aerobatic instruction formally does require an instructor qualification (unless I'm mistaken).
You are mistaken - an instructional qualification is required only to give instruction for a licence or rating or qualification in the licence (ANO Article 36). Since there is no such thing as an aerobatic rating and no aerobatic qualification can be included in a JAA licence, no instructor qualification is required. Interestingly, the privilege to teach aerobatics is not included in any JAA instructional qualification.