You can wait until you are at WDW with your APs in hand for the discount as we did it. We just called the phone #, signed up over the phone and then had them fax a letter confirming our membership to our resort. I am sure that even if you are not staying onsite that they could fax it to your hotel. They can also email it, but I am guessing that even if someone has their computer, it is unlikely that they'll have a printer.