You can get the same effect by just holding the hit in longer, ever play toke toke pass? (or windmills, traffic lights and a whole bunch of other names for it). Take a toke , pass it on and dont breath out until it gets back to you. The longer you hold it in the more effect it has.
We used to play it when i was a student, but i dont think its very good for you. I just prefer a good old joint these days, im not so worried about running out any more