An AP room only rate does not translate to a package booking. The dining plan can be booked only on a room/tickets package, except for DVC members. It can't be added to a room only booking.
As noted, if a package discount is released, an AP holder can book the package with a 1 day base ticket. The ticket never expires and can be used toward the renewal of the AP, or toward the purchase of a new ticket.
I have never seen an AP package discount, but since AP holders don't have to purchase tickets, they couldn't specifically offer them a package. The only way to reserve the dining plan without purchasing any form of ticket is to stay at a DVC resort on points.