Good luck I hope it will be enough for you! I know you say you can't add a venting system. But I have built and advised on building, and have built a smoking lounge in my home. In fact I have built (2) of them in my home.
The first one was down stairs in a formal living room I had enclosed. I used it for over 10 years then I had to give it up to have my mom come live with us so I could be her caregiver. After a year of smoking in the garage I could not take it anymore and I built another smoking lounge upstairs in a loft I had enclosed. But I can tell you the cleaning cigar smoke does not work that well. The only way to do it, is to remove the smoke as fast as you can. What are the chances you could swap rooms with your son.
If you are going to smoke I would definitely use a
Window exhaust fan It wont be that bad with the A/C on and the window fan. If you get one that fits good you are pushing air out not pulling air in. This is my set-up (decorations have changed of the last year but pretty much the same) It has a 1100 CFM ventilation fan in the ceiling that is low sound but changes all the air in the room completely every minute.
(If you need any info LMK)
