To get rid of smoke stink, ozone generators work well. As it would be relatively cheap, easy and non-destructive, I'd start there. Ideally use a commercial unit as it pumps out a ton more than consumer crap. You can probably rent one. Run it for a day or so and then turn it off for a day or so before you go in (or open the door to quickly vent and you can pull it earlier). Ozone won't kill you but it is an irritant and your eyes and lungs may not like you if you go in early.
I've been looking for one to add to the collection of rarely used but very useful tools but haven't found one for a price I am willing to pay yet. It looks like you can rent for 50-100 a day but maybe you can find someone that will lend you one. Most hotels and car rental companies will have at least one to clean up after aholes.
EDIT:
Assuming this is a normal cold room with 2x4" vents, it is surprising that smell persists after so long. We are headed into the wrong season but a fan ducted to either suck or blow off the floor attached to one vent and leaving the other one open will give you a ton of complete air exchanges in a short time. Since it has persisted for so long, I don't have high hopes that this solves the problem. If you were considering painting the room, I would do this for a while first, then a dehumidifier to dry things up for at least a few days, then paint to seal in smell.