I have a combination HDMI switch/audio extractor (similar to the one linked below) so that I can connect my ROKU and DVD player to my surround receiver, which has no HDMI inputs and only has two digital audio inputs (I use one input for the cable box, and the second input is connected to the HDMI switch).

As hokeeron1 said, once you have the audio signal split from the video signal, you can connect the bluetooth transmitter, but that is assuming that you have the sound bar connected to the TV audio output or cable box audio output. With my switch/extractor, the HDMI cable still carries the audio signal with it, even though the audio is also extracted to the optical output port. So in your case, you could have a bluetooth transmitter connected via the optical audio output, and the soundbar could still receive the same audio signal through the HDMI cord. That way you wouldn't have to buy another audio switch, or unplug cords when you wanted to switch between listening methods. Hopefully that makes sense.