I did this with a ADR for Le Cellier for our trip this coming October, we are staying at Port Orleans(PO) French Quarter the first night before starting a 12 night
DVC trip, and my significant other

loves the bread sticks at the Canadian place. I had been checking availability at 6 months out before you could make the ressie and nothing, and I mean nothing, was available, so....... I added on to the existing ressie at PO 9 more days, I had already paid the deposit for 1 night, and off I went to make the ADR, well imagine my surprise... I could pick any time for the ADR I wanted. Well after making the ADR I waited for a week, went back and canceled all additional 9 nights before the actual night, thus leaving us with the ADR and the original one night at PO.
People I know were not happy,

thought I had cheated someone...etc, Disney maybe?

But they haven't seen my wife happily eating bread sticks at Le Cellier.
We are taking our 2 older daughters, ages 39-35, and 3 grand kids for 11 nights next April, and on a whim I checked Le Cellier for room at 6 months. Imagine my surprise, no room. But we aren't staying off DVC the first night so no Le Cellier.
Caio
Moe