Just take a break, man.

That's what I used to do. I'd just take a break for about 4-7 days while working out and drinking water. My breaks were mostly to lower tolerance, but also because I felt I had to stop smoking so much.

And let me tell you, after those breaks, that first hit is the greatest. Tastes so sweet, mouth starts watering, mmmmmm-mhhhhmmmmm!!