Another way to get an AP discount is the following:
Go to Mousesavers.com and subscribe to their monthly newsletter.
In that newsletter there will be a special link to discounts on MYW tickets at several ticket brokers.
Purchase through that link the largest MYW ticket that costs less than an Annual Pass on their website.
(If you are getting regular APs, purchase a 10-day nonexpiring MYW pass)
(If you are getting premium APs, purchase a 10-day with Water Park & Fun nonexpiring MYW pass)
The above tickets provide the largest discount over gate price.
Now, when you arrive at WDW, go to any ticket window at a park and tell them you want to upgrade those tickets to APs or Premium APs).
Disney will give you as value for those tickets their current gate price (regardless of what you paid) and you will only pay a small amount to upgrade.
This is NOT a loophole or tricky backend way to get a discount. I have talked to several CMs at ticket windows and it is simply the way their computer system is currently set up. (DISCLAIMER: It is possible that they could change the computer system at any time, but the way the MYW pricing is set up, it is unlikely for the foreseeable future.)
This only works with unused tickets.