I didn't drain this weekend hoping for more responses.

The tarp would have to be the size of the liner. It can't just be the length and width of the pool because you have to account for the depth...or at least half of the depth depending on the amount you needed to drain - and then some so that you can hold it down on the perimeter of the deck, otherwise it would slide into the pool.
I'm not sure I could find a tarp that large.