It’s a good point about travel agents, they are definitely constrained in this area and so I would be surprised to find a business travel agent who would be willing to book this upfront. That said, omce you have started travel and you change you plans, I have not found AA to be as draconian as some in the thread suggest they might be. I often rebook on a different AA flight with a new ticket when that is more economical (or just plain possible given restrictions in the original RT) and have like another poster above found there are many times when AA will in fact give a (not insignificant) refund to the remainder of the original ticket. Nobody here should be surprised at how often there is a schedule change, delay or other issue that AA deems adequate to trigger a refund.

But a word of caution, even if my TA allowed double booking a return with AA at ticketing time of the original AA RT, i would not do that, I think you are playing with fire doing that.