Big thanks to CDG for the great conversations around this topic as well as the use of his many different lengthed, shaped, clamped, and screwed world of the RAM BALLs .
The hardware:
i) 2xBT dongles with transmitting and receiving capabilities. Must be with low latency ie:
https://www.amazon.com/TaoTronics-Bluetooth-Transmitter-Receiver-Simultaneously/dp/B01EHSX28M
ii) Uniden R1, latest firmware, settings slightly modified from KMPH recommendations as mentioned earlier in this thread.
iii) Ram mounts of assorted types
iv) Cardo Packtalk
v) In-ear safety headphones
vi) In-helmet speakers that came with the Cardo Packtalk
The setup:
On the bike, Uniden R1 connected via 3.5mm jack to BT dongle #1 (BT1) acting as a transmitter. Transmitter is velcro'd to the top of the radar, and the radar is velcro'd to the ram mount plate. RD is hardwired and has a couple of usb micro cables adjoining the stalk for charging of cardo/BT dongles.
On the helmet, Cardo Packtalk is adhesive mounted and will be connected via 3.5mm jack to safety headphones. In-helmet speakers are placed in speaker cavities and connected to the BT dongle #2 (BT2) that is velcro'd to the back of the helmet.
Full Cardo communication is maintained as well as the ability to enjoy music/podcast/whatever at a reasonable volume. Audio alerts from the detector are maintained and one is alerted without having to withdraw visual focus. The detector is mounted on the left side, high and forward, between the visual field height of the mirrors and gauges. It can be reached as well without redirection of visual focus as it is in the lower peripheral field of view.
Speakers are loud enough that others can oftentimes hear the alerts over my Cardo transmissions (via my mic). Thanks to Squisher, I modified your idea with the BT headphones.