Here's a
link to the thread I started back in August that kind of relates to the same topic.
Unfortunately, I never figured out how to do it all online. But Xyzzy's advice works great:
Price the ticket with the flights you want. Use the "pay with cash" option to reserve, call the web support desk and ask them to change the fare class as you wish. Then purchase via the web site. It's fairly easy and you still get 100% EQM.
Hopefully there's a fix in the works to allow this to be done without operator intervention.