Yes, book the QI and when you want to leave just tell them reception what you are doing then they don't think you have gone missing, they won't mind as they can then sell the room again. We have done it and gone on a cruise but was cheaper to pay for a room for the whole holiday.
Also look at Fly drive and booking all your rooms yourself. Hotels like QI can be picked up from about £20-25/night.
Just looked at price for Poly for next year with Hotelopia as ATD are a bit pricey usually. It come up at £1,063 less 10% code £956.70 less 10% cashback with rpoints or Quidco £861.03, Other hotels on there also like Boardwalk or Yacht Club Resort that are cheaper.
Dates may vary in price, that was June.