You do not need a code to book a bounce back. Just call x8844 from your hotel room or you can call the front desk to connect you to reservations. You must book the new reservation while you are still a guest at a Disney property. You cannot book the offer after you check out.
I was just able to book a bounceback on 11/20 by calling the front desk. They connected me to reservations and they told me the offer was 35% off Deluxe or 30% off moderates for select dates. They did not ask me for any PIN code. There was no flyer or notice posted in my room so I guess you just have to know to call and ask.