This might take this discussion in another direction, but back in the late 70s there was a product (called Prolong?) that was sold in camera stores. It was in a spray can of nitrogen or nitrogen mixture of some sort, with a horizontal nozzle that could be directed into the developer bottle. Because nitrogen was heavier than the air in the bottle, it would displace the oxygen at the surface of the developer, keeping it from oxidizing. It worked really well, but I haven't seen it in years. I know you can buy liquid nitrogen now, and a spray bottle, but I think they're rather pricy, and I don't know if it would work.