I've never heard of purchasing APs through AAA, but then again, I don't have AAA so I don't know what options they have available.
As for upgrading your parkhopper, its coded into the ticket how much you paid. DL will scan it, then have you pay the difference for whatever AP you choose. Just be sure to use all your park hopper perks first, then updgrade on your last day. That way you won't lose your early entry, ESPN Zone credit, etc. Also, you don't want to upgrade too early, then not be able to go into the park because its a blackout day. That's why you should upgrade on your last day.