You would need to be pretty familiar with mycology to chime in on this one but I figured I'd throw it out there and see what kind of response I get. Was thinking of having a couple monotubs of Pleurotus mushrooms growing in my closet grow. Basically the idea is that the mushrooms will give off CO2 as they grow, supplementing the females. Since mono-tubs provide their own micro environment I don't think the difference in humidity would be a problem. Monotubs are also self venting so O2/CO2 exchange would be automatic. The question would be, how many 18 gallon monotubs would you need to make a noticeable difference in your grow? Has anybody ever tried this?
They do sell those myco bags, but from what I've heard they are useless. I'm thinking you're going to need a LOT of mushrooms to get the CO2 up to a decent level. You could simply buy one tub and throw it in your room and monitor the CO2 levels. I'm not a mushroom cultivator, but I do know that you should run warmer temperatures when running CO2. From my experience, mushrooms seem to grow in cooler environments. That may cause problems, but I could be wrong.