I've burned with several of my bosses, way back in Noah's Ark days, and never had a problem. Usually, they have too MUCH to lose if they try and start a hassle or something. So, I'd probably say something like "man, I smoked boatloads in high school and college, but it's probably kill me now," and then laugh like hell and see what his reaction was. Then I'd make him take a piss test, LOL, ha, ha, ha...