I know the memnotic adjuster device was already mentioned, but I feel like it would just be easier on everyone to just say "Hey, my guy is joining this order." GM: "Well, they have a strict training regimen, so some of the stuff your guy could do is going to fall by the wayside as he fails to maintain it, but here's your new shiny archetype skills." As long as the roleplay is they, game mechanics shouldn't chain you down. That said, I don't really have a horse in this race at the moment as I'm perfectly fine with the classes currently available and feel no need to modify them.