How can I get  jack/alsa to send output to bluetooth headphones? 
Pulseaudio does it out of the box, but only for those applications which are using pulseaudio as a backend.  What i'm really looking for is:
whilst I'm  mixing in Ardour I use my external soundcard for monitor speakers and headphones, works fine.
Every now and then I would like to switch to bluetooth headphones to compare the sound, so the goal is to have simultaneous output to  bluetooth. If that is not doable basic switching would do of course as well.

I'm aware of the latency , but in my scenario that really does not matter.