Oh lordy - I just had it plugged in while in fastboot mode for half an hour, at which time it spontaneously rebooted. A couple of button presses later and we're back at "please plug me in". This thing really doesn't want to charge, except on that screen apparently. Hoping that's a software thing rather than a problem with the battery, and that I can sneak in a few fastboot commands while it's minimally charged from this screen. D'oh.
I very much appreciate your replies about my nasty case, geekmaster (and knc1 as well). If you found the time to prepare that u-boot image to auto boot into fastboot, letting me try it out with the linux tool, that would be wonderful. (and, if it's easy to do at the same time, another one to revert it back to the main default. And still interested in those "factory" and "reset" modes, again if it's just a quickie recompile.)