Hmm. Another reason to move to kegs???!!!
Just found this note from the Wizard in an old BYO article about using dry ice:
"I get concerned about oxidation and will use methods to remove oxygen from the vessel I am going into. At home when kegs are used, the easiest way to do this is to fill the keg with water and displace the water with carbon dioxide prior to filling.
I recently learned that many winemakers use pelletized dry ice to do the same thing. They place pellets of dry ice in a tank and allow the dry ice to sublime. This forms a nice blanket of carbon dioxide in the bottom of the tank and the wine is filled under the carbon dioxide blanket. This method is easy to use if you have access to small chunks of dry ice. This method requires attention to detail since dry ice in a closed container is a great way to make a little gas bomb. If you choose to try this method, do not place the dry ice in a closed vessel, rather leave the vessel vented to the atmosphere to ensure that pressure is not built up in the carboy, keg or whatever you are using."