Changing Carriers on a reduced fare ticket.
 

I am in Florida visiting my father who has been here for a couple of weeks. I am going home tomorrow, my father is scheduled to leave next week. Yesterday while eating dinner my father hurt himself by kicking a chair as we were at the restaurant. He was thinking about flying home (to Chicago) tomorrow to avoid being in Florida by himself, actually an idea I did stick in his mind since he is 80 years old. I called the EXP desk to try and use his return portion on United on my flight and was told that the only way that this happens is if United would agree to pay AA the full fare value for his remaining discounted fare ticket. I thought I had read somewhere here where it is possible to bring this type of ticket up to the agent and have the switch made. Does anybody know exactly how this works? BTW I do have an alternate plan with an award seat taken from my account for him to fly with me tomorrow. I know that he could fly in the air an hour in front of me to terminal 1 in Chicago, but personally I feel better with him on my flight.