This idea might not make too much sense at first...
Get a NEO6M GPS module connected to a UART on the BBB. Write a quick-and-dirty 2D pythagorean NEMA-compliant routine that determines the distance to each hotspot and then connect to the one that makes the most sense (since radio frequency fields are basically circular on the ground).
A nice side effect is your moving device wouldn't be "promiscuous" if it was out of range of your networks.
Just and idea.