It's easy and it's hardly forbidden, nor is it in dangerous, or wrong. Come on guys. It's called Erotic Hypnosis, you can find a great program on it by David Shade and Major Mark Cunningham.
What you're fully referring to on the NLP aspect is anchoring. I've done it with text messaging, statements, and more with some girlfriends. There's nothing more powerful than being able to send your girl a simple text, turn off your phone, don't respond to any of her text, have her come to your door and tell you that she is soaking wet.
You can do it very quickly doing hypnosis and you can set the anchor anywhere. But if you want to do it without her awareness, it involves actually giving her an orgasm during sex.
For safesty--I urge you to do this process with a WORD and a TOUCH, that way you have to do both to activate it, and you can't accidently activate it. True story, a master hypnotist I know, hypnotized a girl to have an orgasm with a simple grab of her arm, he was dancing with her on the floor, implanting the seeds, getting her hot and bothered, and her boyfriend comes by, pushes him, grabs her arm, and she comes... we had to run out of there... that is unethical.
Touch and Word.
So basically, when she is beginning to orgasm, touch whatever place you want to anchor the orgasm to, and use the word, "Sexxy, Sweets, Hottie," whatever word you want--best to be a nickname for the bedroom. She'll come and the sensation will be there.
If you can do it multiple times, all the better. Then in the morning, simply begin to slowly access that anchor. It'll take a few times to get there, but, eventually, you'll just have grab and say those words and she'll come.