Using apps like Trigger, Tasker or AutomateIt it's possible to do this, but there's an annoying problem:
The rule "If GearFit is disconnected -> Turn off Bluetooth" is applied when I turn on bluetooth to connect the Gear to the phone. So the bluetooth is turned off instantly. I've the same problem with Trigger and AutomateIt, so I don't think is bug related to the app.
Any suggestions? Thx