I like where your mind is going friend. I've been looking for a way to do this myself. In Germany many breweries harvest CO2 production and repurpose it somewhere else. The best analogy for how crazy it is how we do things would be this: It's like fermenting your beer, removing the alcohol like a waste product, and then when the process is finished, add industrial ethanol back to the beer again. We dispel one part of the process, and then buy an industrial form of it (usually a product from electrical generation).
But you can't simply plumb it in to another vessel and call it good. A lot of compounds are leaving the fermenter in gas that we do not want in our beer. The gas would need to be cleaned up with a filter that can handle high humidity and but also dry out perfectly well when not in use. I've considered some kind of CO2 gas carbon filter or perhaps even a tightly packed water filter put inline to bind up some of these compounds and scrub the gas. I haven't gotten around to testing something like this out yet though.
I will say, if you are in the business of reducing CO2 bottle needs spunding valves are well worth the exploration. You can get out those sulfur compounds out of the beer while also carbing your beer 60-80% of the way using the CO2 from the fermentation. This way your bottled gas simply tops it off. Aside from being more resource conservative, ester production is slightly restrained, fermentation completes faster from fluidic convection, and volatile aromas from hops are retained in solution better. There is a research facility in the hop capital of Yakima that spunds all their beer for these reasons and it's some of the best beer made in the state.
