i have a very serious problem

[Danked]

There's nothing you can do, especially if it's a hung ceiling. If it's nice or if you just desperately need the place, the burden is on you to be a good tenent to your friend and colleague. Anything you try is going to be more complicated than just going outside. Lighting candles/incense (just a another smell permeating the floor), using a spoof (damn silly in practice and appearence), smoking by an open window (just circulates it back into the house), etc.