The upgrade process is started by firmware on the empeg that's run before the kernel is loaded. It checks the AC/DC status itself based on the position of the leaf switch inside the AC power socket (it's not actually AC at that point, but you know what I mean). There's not any way to modify this code without physical changes to the empeg, so there's not really any way to change this.

I suppose it might be possible to change the socket in the empeg so that the leaf switch is replaced with a reed switch that could be activated by a magnet or solenoid inside the dock.