Any iPod 30-pin chargers (usb or AC) with 30-pin PASS THRU?

[Mini 9]

I have bluetooth adapter that uses the 30 pin slot.
But for sitting at desk I wish to not discharge battery.
So, wondered if anyone has knowledge of a charger (any type) that allows another 30 pin device to be used while charger OR just using the external energy source for functioning.

Thanks.