Unknown. Some persons on the boards have reported that they were able add the dining plan to a room only reservation without having an AP. Some have reported that they were told they couldn't do that. Disney has made no official announcement regarding the DDP being available for room only bookings of any kind, just for AP holders. How that would mesh with the bounceback reservation is unknown. You would need to call the reservation number and ask.
I tried and was told no. I would have to cancel my room only ressie and book a package, losing my bounceback discount. Upon realizing I could get a nice discount with AAA, I canceled my room only ressie and booked a package through a AAA TA. Since I was staying at a Value resort, it turned out to be the same discount.