Go to any health food store, and buy dandelion leaves (yes, it will resemble pot)
Then go to a tobacco store, buy empty tubes (with filters!) and a automatic roller (so you don't have to deal with rolling and licking and making a general mess).
then, instead of putting tobacco into the roller, you put the dandelion leaves in there, and roll a dandelion cigarette.
No tobacco, you can light it and it will puff and smoke (although it will taste nasty!) and also will comply with many theatre and school standards;' the smoke dissipates fast, and you're not putting anything nasty into your body.
OR...there's also a brand of cigarette called "Eclipse," which are herbal cigarettes, tobacco free, and the smoke dissipates FAST as well and the best part, there really isn't any odor. This is probably the best suggestion, but they can't be found everywhere -- you may have to order them, or purchase them at a specialty tobacco shop. Unfortunately, they taste like a campfire...but they work.
good luck!