You'll probably need to get into the vents as well. Cigarette smoke leaves a residue on just about every surface and you can bet it's inside the ventilation, especially if the recirc button was pushed and air/heat was running while he was smoking. Try renting a carpet cleaner with the upholstery attachment. That should help get it out of the seats, carpet, and headliner.
Other than that? Time. I smoked for quite a few years in my Tacoma until I started commuting on a motorcycle. Over the last 5 years (and I quit 1 1/2 years ago) of not really smoking in it, and keeping it clean, the smell is all but gone.