And AirPort isn't going to do anything useful in this situation, pretty much the only interaction you can get going between an iPad and the AirPort is a wifi connection.

You need something like this:

http://www.hypershop.com/products/iusbport-hd

or one of the mainstream wifi drives like the Seagate and use something like this:

http://www.hackseagatesatellite.com/wordpress/version-3/

N.B. this isn't a recommendation of either approach, I've not personally used either of them