Well the answer here lies in how blue tooth works.
Not all devices have the same blue tooth. The one in question here is A2DP. This allows the blue tooth connection to send 2 channels to a device. Of course the device also needs to meet these specs. Standard ear pierces do not have A2DP because no one anticipated a person wanting to listen with one ear. To my knowledge these is no phone that can send music to a regular headset. The phone itself would have to process the A2DP into HSP ( headset profile ) and then send it.
The ONLY solution to this that I've found is buying a headset with 2 parts and disconnecting the one ( or stick it in your shirt ).
The Platronics Voyager 855 ( no that's not a typo, it's got he same model number as the droid ) is a stereo headset that I've been using for a couple years now. I get around 5-6 hours of music out of a charge and it's actually small enough you can tuck it under a cap and it's out of sight. I know the sound quality isn't the greatest, but it was my best choice when I bought it..
Plantronics Voyager 855 Stereo Bluetooth Headset | Calls & Music
Seems it was discontinued?