Well, the DVC Owner you're renting from would have to add it to the reservation, but I'd assume that as long as you're on the ressie, you're good to go. One thing, though - are they snail mailing baggage tags, etc. to the address of record? If so, that'd be more "landlord" interaction....
I believe you can call MS directly to add DME to your ressie, as long as you have your ressie #. The phone number would be directly on the confirmation you get from the owner, and they could mail the info and tags straight to you, I believe. I believe that Disney wants as many ppl as possible to take advantge of DME, since the more folks they have "stranded" on-site, the more you will buy directly from Disney.
I think you might also be able to set up DME thru your airline or travel agent.