Yea, at check-in you can do this. Or, you can call the USA number at +1 800 882 8122. The website is pretty terrible, and you can't do much (if you don't know mandarin), but when we flew them this past summer we didn't have any issues. Make sure your FF# is printed onto your ticket, if it is not there after you check in, make sure the ticket agent adds it - just give her your card and point to the *A logo or something.

Be prepared for an interesting experience, where they load you onto a plane, then delay the flight six hours, and only say "we will tell you soon when we leave." And people think flying in the US is bad!