How To: Bluetooth audio through Mono headsets
 

There is probably an easier way but this is how I am listening to music and all other audio through my Bluetooth hands free mono headset.

First you will need the ID Transfer cab found HERE thanks to Bad Sector for making this for us. MSCV is used in the ID transfer to Bluetooth and there are problems with that on the Mogul so I wont go in to that here.

First make sure you have at least 2 places available on the start menu, than load the cab to the device after that you will see this on your Start Menu.

http://upload9.postimage.org/123565/sshot001.jpg

Notice the Audio and ID Transfer the audio is what we want.

Next I get rid of what I don't need so go to File Explored/Program Files you will see this

http://upload9.postimage.org/123704/sshot002.jpg

Delete these 2 items it will say that ID Transfer file is a program select yes to delete.

Next still in File Explorer got to Windows/Start Menu you will see this

http://upload9.postimage.org/123755/sshot003.jpg

Delete ID Transfer

Next still in File Explorer go to Windows/Start Up you will see this

http://upload9.postimage.org/123812/sshot004.jpg

Again delete ID Transfer

Now all we need to do is turn off Voice Dial by going to Start/Settings/Voice Dial/Settings and set to Disable

http://upload9.postimage.org/123845/sshot005.jpg

Now to start the audio turn on Bluetooth and make sure the Bluetooth device is paired with the Mogul. Go to Start and select audio to open the audio gateway, now all the audio from the Mogul will be coming through the Bluetooth device, to disconnect just turn off Bluetooth or turn off the device. That's it 8)

I have used this for a while and it will also work on all the AKU's I tested on the 6700 but you will need to disable the Voice Command through the registry, if anyone is interested let me know and I will try to find the file path and post it.

does this enable custom ringtones to ring through to the headset?

It will because all audio goes to the bluetooth, but that's not really practical for this as soon as you turn off your PPC the Bluetooth will disconnect, I just use this to listen to music or watch movies.

Easier Solution Found
 

I got it working using a cab someone created over at XDA. It does disable using voice command by simply pressing the button on your headset. However, you can still press the voice command button on the side and either speak into the phone or the headset.

I am not sure what other side effects it has, but it does work simply by installing the cab. I would suggest a backup first if you haven't already. Also, the sound redirect only works if you are not in silent/vibrate mode (you must see the speaker icon).

Bluetooth Mono Headset + Redirect sound to it (cab) - xda-developers