I'll need to do the same, and get a USB port from the radio output, is it possible as well ?
I believe this is a Concert 3, right ?
My thing would be, enable the aux, and plug the Sony Bluetooth Music receiver BM 100
that will provide output of 2 RCA (L+R)(that it would connect to the radio.)but it will need a micro usb input power (500 mA) ...
and then plug it into the BM10 bluetooth from sony.
I contacted the seller to try to understand the output of the USB port, mA, and voltage, so I could plug it into the Bluetooth box... avoiding any extra wiring to be done.