Force music through USB DAC even when BT a2dp connected?

I have a nexus7 installed in my car with the custom Timur OTG+Charge kernel. I can play music fine through a USB DAC via OTG.
When I pair the tablet to a bt a2dp device, all music gets routed to the a2dp device and nothing through the USB DAC.
What I want to do is force all music to keep playing through the USB DAC even when an a2dp device is paired.
I have paid for the pro version thinking this would do it but I can't seem to get it to do what I want no matter what settings I try.
I know it may sound weird what I'm asking to do, but I just need this configuration to work. Is it possible with your app?

Thanks-
Colin

I haven't had time to answer questions in a while.

You probably can't automate it, but you could either:

1) Switch the "Media audio" setting to "USB Host"
2) Leave "Media audio" setting on "Let App decide",
but set "Connectable devices" / "Bluetooth Settings" / Media audio behavior" / "Bluetooth (A2DP) auto usage" to OFF (unchecked).