ETPS are in a rather strange position as I see it.
I recently had to get my head around all of this. They are actually a business area within QinetiQ Ltd who are now a fully private commercial company, albeit with the MOD as a majority shareholder. Civvie aircrew there are company employees, not civil servants.
I am sure that if you can indeed afford the several hundreds of thousands of pounds (guessing here a bit!) required to do the course that the Chief Executive of QinetiQ Ltd will be only too glad to take your bankers draft give you a crack of the whip.
The Sqn would still probably black ball you however but as I say, from a business point of view, ETPS are in a very strange position.