You can't on the atpl either. You do the study, pass the theoretical exams, then go and do the flying. If you look at ESSAR 5, you will find that the majority of differences are related to the theory stuff. No one is arguing about bypassing the practical sim stuff (which, after all, is probably the most important bit), the discussion is about how to convert. There is no practical reason why someone couldn't set up the equivalent of Bristol GS with students then buying their sim time (complete with practical examination) somewhere else. It just hasn't been done, probably because no one sees the business imperative.