My question is how do you get around the problem of the on-board charger needing to be plugged in at the same time? From my minimal experience of level 2 charging points in the UK (i've looked at one), they only offer one Mennekes filler plug (?) and no UK three pin socket for the kettle lead.
In a similar vein, if there is only one three pin socket to charge from, is it possible to plug the super charger into the socket and make the most of the 3kW output that they can provide? I guess you'd need an output on the Diginow that supplies 240v to the on-board charger via a kettle lead. I've also wondered about this with the Elcons too.
You have pins 38/40 on your MBB There is a small connector left of the contactor on battery with connecting to your anderson sbs75x (doesn't apply for non-MY13 bikes) ... these go to your Anderson external charger connector. When you plug in an external connector it talks to the bike to let it know it wan'ts to charger.
In this way you do NOT need the stock charger to put the bike into charge mode. And with this charger, since Brandon is smart enough to realize all you need is a resistor to trigger this behavior, you do not need to have an onboard charger to use the external one.
That said if you really really wanted to keep your external charger there would not be nothing stopping you from making a Y splitter to feed both your super charger and your stock charger. Right now,
since I don't have the 38/40 pins installed on my bike yet (though I have the parts), I do just this with my RSP2000 charging stack.