As far as I know, the DDP for MYW and the DDP for AP holders are the same plan, I'm not sure what you're asking?
EDIT: I checked, the only difference between the two is you have to buy a MYW ticket with the MYW plan, whereas the AP plan you already have tickets.
Correct. There's an Annual Passholder package plus Dining that is the exact same as the regular MYW plus Dining, but it just removes the ticket requirement. And though it's highly unlikely that there'd be any AP discounts that close to Christmas, if you did get a discount you could add the Dining Plan to it.
But, if you'll have the Annual Pass, there's yet another option: Tables in Wonderland (formerly the Disney Dining Experience). For an annual fee (I think it's $65), you get a discount card that's good for 20% food, drinks and alcohol at most Table Service restaurants in WDW, and it's good for up to a group of 10 Guests. If you eat at a lot of Table Service places, it might be a more flexible option than the Dining Plan. It's worth it to figure out how your family would use it. (I did the calculations for how me and my friends would eat, and the TIW came out ahead of the Dining Plan every time, except for when the Dining Plan was free)
Which brings me to my last point... If you book your next trip under a discount that you MUST book as a package with tickets (like Free Dining, or if this B4G3 promotion reappears in the future), you can book the package with 1-day tickets to fulfill the ticket requirement. You can then save that 1-day ticket until your next trip, when you can upgrade it to a longer ticket, use it to renew your Annual Pass, etc.
That's exactly what I'm doing. Back in September, friends and I went down to WDW under the Free Dining promotion. I upgraded my ticket to an Annual Pass. Now, my roommate and I are going back down in June, once again under Free Dining (I got a PIN code special offer email). It's booked with 1-day tickets. My roommate will upgrade his to a 7-day ticket for use that week, and I'll save my 1-day ticket for some point in the future.
-Rob