Can you gradually replace tobacco with weed?

[runawayahhhhh]

Hey guys, I have been smoking cigs/cigars/pipe tobacco since I first turned 17 two years ago. I smoke weed whenever I feel, but can't quit cigarettes. I can go without weed for weeks at a time and not care, but 5 hours without a cigarette and I am ready to burst. Now I don't want to hear anti-activists. I also have been substituting weed for vicodin, which I am prescribed for chronic pain. The weed works better, and I don't get a "hangover" feeling like I do with vicodin.
Oh yes and if it helps I smoke 4-10 cigarettes a day. Marlboro Reds.