Vacation Club owners can do this because they don't have to book packages - their reservation system is completely different from the CRO system where you must book a package with tickets to get a dining plan.
There are some exceptions - annual passholders and those eligible for the military discounted rooms may book ticketless packages. There are some rumors going around that ticketless packages can be booked by guests who are not AP holders or military but you'd have to call WDW reservations and ask about a ticketless room/dining package to know for sure.
If you are booking a DVC points reservation you do NOT need to purchase tickets at all to add a dining plan.
If you are "renting" points from a member, YOU cannot add the dining plan to the reservation. The member must call Member Services and add it for you. Member Services will not speak to you if you don't have a DVC membership number. Right now the DVC dining plans are paid for in full at check-in, but they are looking to revise the system so that dining plans must be paid at the time they are added to the reservation. That hasn't happened yet, but when it does, it means the member will have to pay for the plan and the renter reimburse the member.