When you go to the airport to have it done, budget a lot of time.

I did it the middle of last year for a simple itinerary using an AMEX gift card and a credit card as my two forms of payment (two is the maximum AA will accept) and it took nearly an hour.

Everyone on line behind me waiting to check in was sending daggers into my back with their eyes. Don't even try it at an airport with a small AA presence. The counter agents just don't have the time to do it.