Question [Q]

Asked this question on the nexus 5 forum, but no answer so I thought I'd ask here too as I have the same issue on my Nexus 4.

When connected to a bluetooth device in car mode, I'd like to force all audio to the car bluetooth speakers and mute the internal speakers. Problem is, I don't see a mechanism to mute the internal speakers while not affecting the bluetooth volume in either Llama or Tasker. Does anyone know how this could be done or a Tasker/Locale plugin that has this functionality?