In these cases you never even have to talk to any agent or human.

After you land at whatever the final stop will be, just pull up your reservation at aa.com and cancel it. You can do this even after you're checked in. You will be removed from any subsequent flights on the PNR, it will not be repriced, and no one will ever look at the PNR again. This saves the GA from looking for you and paging you in the airport or waiting until the last minute to open up your seat.