The AA app - whether or not you're logged in as a member - gives the option to SDC either on standby or a confirmed reservation. I used it this week on a domestic flight, it's excellent. Not sure if it's allowed in basic economy but as a OWE you can fly basic economy with bags and main cabin plus seat so I'd be inclined to think the option is available.

Also in the app is the ability to bid on compensation for oversold flights should you choose to take a later one.

Very slick.