The level 58 thing isn't actually true, you do need to be level 50 to get training beyond 300, but the level 58 issue is for going through the gate, not for leveling to master crafter. If you want to level your crafting past 300 before level 58, you will need to have someone summon or port you to Shattrah so you can run out to honour hold (I recommend doing this naked since I have yet to survive the trip :P)
At least this has been my experience as a level 55 with JC 355