I am going to answer this with complete sincerity and careful detail. This is because I have met some smokers who have no idea how to breath the smoke directly from mouth to nose without going into the lungs.
I've seen people knit their brows and try to do it and end up coughing. It's difficult to explain how to do this. I just sort of taught myself. The nose hit is definitely a part of replacing the analog experience for me. Here is my take on this:
It doesn't involve breathing or using your diaphragm in any way. Relax your stomach muscles, they have no part in the basic steps. neither do your lungs until you have mastered the basics.
This is very similar in many ways to sucking in liquid from a drinking straw before swallowing it, but with vapor instead of liquid, and pushing it into your nose instead of swallowing, which is why I will keep referring back to that process. Hopefully almost everyone reading this knows how to use a drinking straw.
1. Close off your mouth from your lungs and nose by pushing the base of your tongue against the throat hole at the back of your mouth, as though preparing to drink from a straw.
2. at the same time, press your tongue flat against the roof of your mouth.
3. Put the eCig tip in your mouth just like you would a straw tip in a drinking glass.
4. Draw the vapor into your mouth in the same way you would draw liquid into your mouth from a drinking straw, by pulling your tongue slowly down and creating a space between the roof of your mouth and your tongue. Remember while you are doing this to keep the base of your tongue pulled back, covering your throat hole. Just like you are sucking in liquid from a drinking straw.
5. Remove the tip of the eCig from your mouth, keeping your lips closed.
5. Now, relax the base of your tongue and let your throat hole become uncovered as you do just prior to swallowing a mouthful of liquid drawn in from a straw, but do not breathe in at all. keep your diaphragm still.
6. Holding your diaphragm still and your lilps together, push your tongue up to the roof of your mouth. The vapor should all be pushed out of your nostrils.
That is all there is to it! Practice a few times step by step. Take a big breath first so you will be able to hold your breath for a few seconds while you go methodically through the steps.
When you have mastered the basics, you can work on very slowly exhaling while pushing the vapor out of your mouth. The mixture of air with vapor can enhance the nose hit sensation significantly in my experience.
This doesn't just give a nose hit with nicotine, it also lets you taste and smell the flavor of the eliquid much more. And try it with a strong menthol flavor, it is a very cool nice sensation. Enjoy!