Ac / heating question?

My office heating/air conditioning duct work was expanded to include a small kitchen & another 20x15 room. No returns were added to the extra ducts (or whatever you call them). The guy who works in the room is a chain smoker. Shortly after the ducts were added I started smelling smoke in my office. I'm told I'm crazy and that it's impossible for smoke smell to come in since there's no return in that room. I said smoke can still go up through the vent and travel. They closed the vent & that didn't work & he covered the hole with a piece of metal, but it's not sealed & I still smell cigarettes when he's smoking a lot. Now he has a fan to keep cool & it's blowing the smoke, up at the ceiling. When the guy isn't here, the smell isn't here. I say the smoke still gets in and travels through the duct and they say I'm nuts. Please help. I'm desperate & hate smelling smoke in my office everyday. What is your professional opinion??