idk if you figured it out on the Lumiose City boutique yet, but, I did a little more digging around to see how to access that one in Lumiose, turns out you have to do a little bit of everything in the city. Visit a lot of cafes, do a few battles here and there, try out the Institute, odd jobs in hotel, dining in restaurants; you just have to do a LOT of the things there, not really everything, and then they'll let you in once you're "cultured".