There is no 'trick'. You need to start from zero Asia Miles like the rest of us.

Your chances might be better if you join MPC. That's $50.
http://www.flyertalk.com/forum/15321393-post12.html
Read from 10.1

Then you may try to ask for a status match to at least MPC Silver.
http://www.flyertalk.com/forum/catha...tus-match.html
With CX MPC Silver, you get lounge access when flying on CX.

Then each and every time you fly, you need to book on CX metal, CX flight number and credit your miles to MPC/Asia Miles. Then your upgrade chances are better but never guaranteed. If you book on AA flight number, your chances of any possible op-ups are greatly reduced.