He could probably use CO2 at 90ºF (32.2ºC), but I don't think a CO2 bag in there will do much to happy up the plants. I'd be happy to be proved wrong though!
You have to run it up way past very harmful to human levels (4000pm) before it becomes a detriment it my understanding. The higher temps, light levels, Rh are lacking its just a waste of perfectly good Co2 deployed ineffectively is my understanding. But some bags aren’t gonna hurt. Its just naturally composting organic matter like in nature.
Nick