Not sure if you can, but if you can the cost is $32.00/night.
Going from your other post - What you probably want to do is really look at what you and your DH want to eat when you are there and add up the menu prices. The DDP and the DxDDP can be a great deal, or you can end up spending more with them than without them. It really truly depends on how you eat. Not just where, but also what you think you'd normally order.
LAst time we went LAnd/SEA DDP was not available if you booked the "land/Sea package" through Disney..Better call and make sure it is available. We cancelled our "package" and booked land /sea seperate to get free dining and made out better