Automatically change volume when Bluetooth disconnected

Hello all,

I recently purchased a device which allows my iPhone music through my car wirelessly. This is accomplished by connecting via Bluetooth and this signal is then sent through the AUX port on in my car. I turn my volume on my phone up to max to allow the best quality through the bluetooth device. When I disconnect, however, my phone stays at this volume. I would like it to treat this device as it treats headphones and have a volume set of this and a volume set for the normal iPhone speakers. If anyone knows how this would be accomplished it would be much appreciated.