Amigopod can handle the email registration and confirmation. You will have to grab the MAC address (which Amigopod can also do for you) for the "permanent" registration. If you use only email authentication, the controller will time-out every so often and the user will be forced back through the captive portal login. If you grab the MAC address and then do MAC authetnication via Amigopod, the user wont have to authenticate until the registration expires.
Maybe Cam or one of the other Amigopod experts can shoot you a link to the setup guide for MAC registration and authentication.