Pali, I have tried USB mode with charging with an external HDD and battery pod; I got an error "charger attached" and it refused to allow the connection putting me back in the peripheral mode and charging starts.

Now that I am used to getting connected over 95% of the time using a flash drive (vs ~30% connect on first try with h-e-n) and have a custom swappolube profile for big USB transfers I don't bother with moving big files over wifi anymore.
Kickass work Pali!