It's kind of a pain. Honestly at this point, with the Pokébank update and all-- I'm thinking I might just transfer them to bank then X, train em, and bring em' back haha.
I use the Poke Peligo island Poke Evelup to max out their stats or raise their stat to certain point and then use the EV berries found on Route 10 to lower their stats to the right point.