If you are booking a OneWorld Award and you are SG or WP then go for Dave Noble's suggestion book the trip with the dates available and change them later.

As a SG or WP you won't be charged a rebooking fee. This is exactly what I did a few months ago. You will have the initial 2,500 fee however (which you will almost have anyway if it is an interesting trip with different OneWorld members).

Good luck.