There is no magic in black pepper EO. The only thing that does for you is to give you something to fulfill the hand to mouth action. This is more or less the same as chewing on straws, sucking an empty e-cig, chewing ice (bad for teeth, but free of calories), chewing on regular toothpicks, eating candy or food (bad for teeth and weight), or anything else that gives your hand and your mouth something to do at the same time.
I quit smoking before there was such a thing as e-cigs. It is tough. No matter what you do, you have two addictions. The first is the physical addiction to nicotine, which can be satisfied through any of the nicotine replacement methods out there: e-cig, patch, gum, lozenge, etc. The other, and by far the worst, is the hand to mouth addiction. That can also be met with the e-cig, or any method I mentioned above. The reason the e-cigs are so successful is because it meets both addictions.
If they HAVE to stop vaping, I would suggest they buy lots of celery, cut it into sticks and eat a stick every time they get a craving. It is the only food that takes more calories to process than you get from it, and it gives that hand to mouth satisfaction.