As others have said, if you want to be aircrew why not apply for it?
One fairly obscure but proven route you could take if you weren't successful would be to join as an airman on the shortest engagement (I've no idea what that would be these days, it was three years when I were a lad) learn to fly at low cost at one of the many RAF flying clubs dotted around and go civvy. I've known one or two over the years that have done this, most recently an SAC gunner who went from first flight for his PPL to RH seat for a LoCo in around two years.