Just tell them that you had a fantastic experience and need some pictures to remember them by for your next visit!
I have personally never had any problems taking pictures of the WGs that operate in the Clubs in Wan Chai. It might be bit more expensive, but easier to spend your time finding the perfect girl and you can discuss all your wishes over a drink before leaving for your hotel.
Usually I pay $1000 and get everything without having to ask (including overnight stay). Multiple shots, pictures, and all the service I like (I am not into kinky shit, so don´t know anything about that).
Only thing they ask for more money is partner sharing with another bro... and cab money when they finally leave at 2 p.m.