I don't know how much CO2 you would need to see any benifits but what the hell. I can buy 40 16gr CO2 cartridges for any where from $20.00 to $40.00 bucks for a box of 40.
Maybe my next indoor grow will include a hole for the barrel of my CO2 pistol. I can just shut off the fans and fire it unloaded into the box. Might be a nice lttle burst of fresh air for plants. Now if you had paint ball air canisters loaded with CO2 than you could really pour it on.
I doubt you would notice a difference even if there might be one
but it would be worth the try. I have read about high heat and CO2 but as hot as my grow box got without supplemental the plants did fine. I think there is room on both ends of the "accepted" temps ranges for MJ. I think it's far more tolerant than folks give it credit for IF there are not a lot of additional stressors.
Stuck without an active grow but just about ready to fire up the stuff for outdoors. Have also scoped out my prepped sites and hopefully can get 6 or 8 plants out. We will see but it easy to grow outdoors but tough to find places to do it. If a spot looks good to you chances are it looks good to someone else. At least I get to follow your grow dank and it's looking awful sweet even with your temp swings. Looks so good I'm not sure you need to do anything different at this point. Rock on and thanks for letting me follow.