I remember seeing some chatter about tunneling over XMPP. Most plane wifi allows chat protocols, and it should be possible to encapsulate your traffic as ascii text in XMPP packets. You "just" need to set up the endpoints to do the bridging.

Of I were to do it, I'd run a a script that sets up a tun/tap interface that everything else on my laptop will communicate through. This script also connects to my xmpp server at home. Any data coming in on the tun/tap is encoded to ascii strings and sent as chat messages to my xmpp server. The same script can also do the reverse. At home a similar script does, mirroring that on my laptop. Make sure prerouting is set up accordingly in both ends.

From what I've seen on planes, it's mostly down to captive portals using mac addresses to track clients. In theory it should also be able to sneak through by spoofing hardware addresses of someone who's paid for the service.