USB A to A will definitely not work. All of the USB ports are connected through internal SMSC 4-port hubs. There are two hubs in the unit, one in the back with 3 ports going to external connectors, and one going to the WLAN module. Up front there is another 4-port hub going to the front USB connector, and presumably to a BT module, but I didn't take mine far enough apart to be sure.
There is one large connector over near the CPU that might have some debug stuff on it.There are also about three 4-pin connectors populated, one of which might be a UART. There is also a footprint for another. Tomorrow I'll get my oscilloscope out and see if any of those pins wiggle on boot.