I haven't gotten Bluetooth working on my RPi yet (still waiting for the adapter to arrive), but I would assume it would work similar to Bluetooth on "regular" Windows...you just need to pair with the audio device.
With other Windows devices I have, once paired, the audio is re-routed through the Bluetooth connection by default. I have used one of these http://www.amazon.com/gp/product/B004VM1T5S to connect to my home stereo to my Surface Pro and that is how it worked.
Once I get my Bluetooth adapter for the RPi, I will try it with that as well.
You can configure the Bluetooth devices on the RPi by connecting your browser to
(or launch the browser through the WindowsIoTCoreWatcher and select the Bluetooth page)
The text on the page implies that just visiting that page will put the Pi in to pairing mode and it will start scanning for devices.
If you have already gotten that far, perhaps you can post more detail about what point your are stuck at.
Update: I received my BT adaptor and was able to get a set of Bluetooth headphones paired with the RPi. However I have been unable to output audio to the headphones yet. I wrote a quick test app just to play some system sounds, and it will play sounds to the audio jack, but not to the headphones. I suspect I have to switch the default audio device, but I haven't figured out how to do that yet. If I figure it out, I will update here again.