I don't get why they don't watermark the papers with each ATO name or who the papers are issued to. They are obviously printing them on an individual basis rather than mass producing so that'd be a very simple first step to prevent them leaking.
Those whose papers appear in the public domain would be ineligible to receive papers in the future.
Also, the CAA has a vehicle for the exam delivery it wouldn't take much for them to deliver E-PPL exams.
In fact some countries get very confused when they get an application with the PPL exams signed off by a GR as most other countries the PPL exams are only administered centrally by the CA.