<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by FlyByMike:
You could possibly sign up for the Gold and the Platinum challenge at the same time, so that you'll get 25% bonus miles between the time you hit 5000 points but before you get 10000 points.</font>
FWIW, I don't recall these rumors ever been substantiated. The "official line" from AA is that you must choose one or the other.