USB OTG media headset and BT Phone microphone - how?

I have a setup that makes perfect sense for a motorcycle rider. Phone calls are managed by a BT device and this works fine. My case is a bit of a twist. Use a BT device for the microphone for phone calls, but have audio run through USB Host at all times.
Q
1. BT headset that has a microphone in the helmet. I want the microphone/voice to come from the BT device, but NOT the audio output from the phone call (really the audio output of BT).

I am able to get the BT device to answer a call and transmit voice, but I can tell it wants to output the audio back through BT, but I have no headphones connected. No headphones because I can't stop, take off the helmet, and put on a real headset. I keep a set of high quality IEM headphones that I connect to the phone so the media audio is best.

2. All audio output (media, notifications, phone...) to play through the USB Host. I have a USB OTG device with a DAC attached and the headphones to it.

Help/Question: How to configure SA Pro (2675) so when a phone call comes in: The phone commands and voice come from the BT device but every single audio/media output sound is always run through the USB Host (I assume host and not client b/c there is no input from USB, only output)'ll

Side note: I'll look more, but when the BT device does tell the phone to pick up, it happens immediately. The microphone doesn't kick-in for 15 seconds so people drop the call thinking nobody is there.

Any thoughts on how to connect to a2dp bluetooth phone so microphone comes in over bluetooth and audio goes out through USB Host?

Once the phone starts ringing, and a Bluetooth mono phone device is connected, that Bluetooth device is forced to control both audio input and output. The headset can't send audio through the mic but have audio output go through another device. The Android audio policy manager enforces this.

It is the same reason this thread won't work:
https://soundabout.forumotion.com/t789-can-i-get-audio-over-bluetooth-but-use-the-phone-microphone