if this is just for the wedding, ie one time, and all the beer is likely to be consumed, sure you could use air. especially if you only do one 5er at a time and not spoil one that doesn't get tapped. however, getting a decent air source i think would be more of a hassle than co2. i would find a welding or gas supply shop and borrow, rent for the day. you will be much better off, then if one is not consumed bottle the rest and cap right on the foam out of the keg.