Go to radio shack and get a 120 VAC to DC converter. Like this one, [link=http://www.radioshack.com/product/index.jsp?productId=2049690&cp=2032056.2032136.203 2153&pg=2&parentPage=family]Radio Shack DC converter[/link].
Make sure you set it for 9 volts. If it supplies 12 volts, I think it does, you can try that if 9 doesn't work.

Remove the battery altogether, and solder a futaba power connector to you new converter, or make a dongle or whatever. Cut a hole or notch in your battery cover so your new cord can hang out. Plug the Futaba side or you converter in to your buddy box, and the other side to the wall. Plug in your converter, turn on your radio and fly away! Not really a hard modification, with a little electronic experience, you should be fine.