Dave, I have been an analytical chemist for over 12 years and preventing reagents from oxidizing during storage is a common problem in laboratories. Here is some practical advice for you. The goal in preventing oxidation in stored developer is to remove the oxygen that is present in the headspace of the container. This can be done by either removing the headspace (such as the marbles technique mentioned earlier or by using collapsable containers). A more common method is displacing the container's atmosphere with an inert one. Two of the most common gasses that can be used are nitrogen or helium which can be purchased from any local welding supply store. Compressed nitrogen can also be purchased from gourmet wine shops which sell small cylinders of compressed nitrogen to prevent partially filled wine bottles from oxidizing.(posted 8570 days ago)If you are in a pinch, you may try using compressed Freon which is commonly used to blow away dust. Check the label to ensure that it does not contain air. Most fluorocarbons are chemically inert and will not react with the developer.
There was one suggestion that recommended compressed carbon dioxide. I would strongly recommend not using CO2. Although it would be effective in displacing the oxygen, the CO2 will dissolve in the developer and form carbonic acid thus lowering the pH of the developer.
I hope you find these suggestions helpful.