You won't be able to directly do it. I haven't decided yet if I will enabled the moment you can go to henosis (first time) or to have it unlock after you at least did the "main dungeon" on henosis.
Ohh, so is it not something you just go in and out of by taking off and putting on her clothes? Sounds great to me either way! As for when it can be enabled, I think should be whenever it makes the most sense to you. Though the sooner the better imo, lol!
The way it will work is, the moment you take off your clothes, the NPC behavior will switch. You put the clothes back on and the NPCs will reset. Just a matter of when I will allow players to take off the clothes.