You could purchase a y fare or a business class fare and upgrade using AA mioes- do it all the time.

Mind you the best deal is to contact www.1st-air.net and get a discounted BC fare and then use 40,000 miles to upgrade- well worth it. Don't forget to register with AA for the Repeat promo prior to flying CX and with comp status with AA, you can get more than the 40,000 miles you will spend