It would fill the space with CO2 but the extreme cold could cause ice crystals to form in the wine. I'm not sure i want to subject my carboy to the fast temp change.
I do not think it would take much, just a few small chunks after it came out of the secondary. Just throw some pieces in the carboy, put the air lock on, and no more air or oxidation to worry about
Air will always mix in with the CO2, its physics, and you cant change physics. Will it help, yes, but not for the long term needed to age wine. Top up or get a smaller carboy.