You can add DDP, but do the math before you do....
Cost is around $52 per adult. If you paid cash on your own, figure $4 for the snack, and around $12 for lunch. That means that you'd have to order a dinner that is $36 to break even. Pretty much every restaurant that I've seen with entrees in the high $30's low $40's require 2 dining credits.
Perhaps I'm glossing over the fact that you get dessert included, kids are cheaper etc.... just sayin' it seems like you could put the cost of the DDP on a pre-paid visa, eat whatever you want all week, and I bet you'd have money left over on the card.