Passmethesickbag

I have a ticket LHR-DFW-CLL-DFW-LHR. The potential need has arisen for me to visit one of AA's Brazilian gateways immediately after my ticketed return date. Rather than flying all the way across the Atlantic and then back again, it seems to be that the most sensible solution would be to change my return date, and then buy a second ticket Small US airport-DFW-MIA-Brazil-MIA-DFW-CLL, and then turn around and go back again with my original return ticket. I have a few questions:

1. Would this fall foul of any rules (I've never quite understood what nested ticketing means)?

2. I presume that there would be no way of avoiding having to fly all the way Brazil-MIA-DFW-CLL and then, using my other ticket, CLL-DFW-LHR, since my ticket is restricted, right?

3. If I manage to travel without a checked bag, would I be able to turn around on the same plane that took me to CLL? It's a 30-minute turnaround. I imagine this would not be without risk, as the bag would likely be big enough to warrant gate check on an ER4 cropduster.

4. If I do check a bag, there is obviously no way of claiming and rechecking it in 30 minutes, even at a small airport. Is there any chance, though, that a switched-on agent, possibly when I start my journey in Brazil but more likely when I re-check after clearing customs at MIA, could be persuaded to tag my bag MIA-DFW-LHR, even though it's too tickets and means skipping two of the segments I'm travelling on?

I have a feeling the answer will be that my only option is to spend four hours enjoying the delights of Easterbrook airport, but I thought I'd ask at least.