I don't smoke, but I dip. I've tried quitting more times than I remember. I even had an entire year free of nicotine at one point. Here's what I observed over that time... I am not trying to discourage you, just something to be prepared for.
You'll feel better, but not entirely better, and it takes months. The physical side literally only takes a few weeks, but the poorly understood brain chemistry associated with addiction did me in. I think after years of pummeling my synapses with nicotine (a powerful poison with a lethal dose less than that of arsenic) I had utterly destroyed my "reward/pleasure" mechanism, which is, I believe, associated with dopamine. Everything was dull, I gained zero satisfaction from normally rewarding activities. I would have been diagnosed as depressed, but since I'm a pilot I don't get depressed.
At this point, the "gum" went over the counter. I actually bought the gum to abuse it! The irony is painful. From the gum I went back to full-blown dipping.
I was sick at heart. Then I did a bit of research. Check this guy (Dr. Rodu) out:
http://main.uab.edu/smokersonly/show.asp?durki=63612
He presents strong arguments that it is the combustion products which kill, and the dangers of smokeless are hugely overblown. There are some Scandinavian countries where 50% of the adult males dip, and their oral cancer rates are no higher than any other country. His basic premise is that if you simply cannot quit smoking, try to use smokeless as a nicotine delivery vehicle. I'm not trying to plug anything. If you can quit, do it. But after a year I still felt like shiite.
No I don't use a spit cup in the cockpit, I don't have a big line in my mouth. I can dip in total stealth and no one would ever know.
Good luck, I hope you guys make it. I couldn't.