In my post I specifically said the 6th thru the 12th as that was what's available. But to save the room, you would need to book those dates and then call back and cancel the last day -- then you'd have exactly what you wanted...the 6th thru the 11th without having to change resorts midstream.
That may be the only thing you can do *at this point* if you want to guarantee your full stay at the Poly. Honestly, if it we me I'd just book it online, pay the deposit and call immediately to cancel the first reservation. If you time it right, the first deposit would be credited on the same statement as the second deposit and it will be a wash.