When I tried to book our DP, I was told to call back after I had made my hotel ressies. They wouldn't give me much info until then. Which leads me to believe it may be mandatory to stay onsite. I was actually a little disappointed, because we are staying dvc and had to wait until 11 months out, we were left with only a few locations still available to choose from. I am very fortunate though, that we got my 2nd choice.
Good luck. Perhaps if someone in the party is staying onsite you could put the DP ressie under their name?