Yes,
DVC Member Services can add the dining plan when you make the original reservation. They can also add it on later, up to 48 hours before your check in date. In all cases, you pay for the plan when you check in.
If you're the DVC member, you can call Member Services and make dining reservations 180 days from your check-in date for your entire stay (of up to 10 days). If you're renting points, though, DVC Member Services will not talk to you. They'll only talk to the member you're renting from. In most cases, the member probably isn't going to want to deal with booking your ADRs for you.
Anyone can call the central resevation office at 407-WDW-DINE to make dining reservations 180 days from the date you want to dine. For a DVC reservation, though, CRO will not recognize the reservation number and you won't be able to do the 180 + 10 booking.