You can fax the Poly four days before your trip to request a certain building. I did that back in August, and got exactly what we wanted. The fax number is: 407-824-3174.
I don't know if they take requests by phone, but the direct number for the Polynesian is: 407-824-2000.
Did you make any room requests with CRO when you made your reservation? That works sometimes, too.
Good luck, and have a great stay!
Karen