My notes on this promo say travel needs to be booked by 9/5 and flown by 9/30, so you might want to confirm the date requirements first -
Book travel to anywhere we fly August 1 - September 5, 2011
Travel August 1 – September 30, 2011
Earn 500 bonus miles when you use your MasterCard card
Earn 1,000 bonus miles when you use your US Airways MasterCard card