nitrogen would indeed work better...and gets used a lot commercially.
a layer of CO2 will still help slow oxidation/staleness a bit though if its all you've got.
I mean, a dime's worth of CO2...its worth a shot!
Primary: English Mild
On tap: Pale Ale, Lancelot's Wheat, English Brown Ale, Steam Beer, HoovNuts IPA
Bottled: MOAM, Braggot, Raspberry Melomel, Merlot, Apfelwein, Pyment, Sweet mead, Cabernet
Gal in 2009: 27, Gal in 2010: 34, Gal in 2011: 13, Gal in 2012: 10