OS X Lion launches iTunes when connecting a Bluetooth Headset
It is completely stupid and seemingly unrelated but it works:
In the CDs and DVDs preference pane disable iTunes to launch inserted for Audio CDs
your headset is an audio cd you know ;-)
What I did is renaming itunes using
sudo mv /Applications/iTunes.app /Applications/iTunesBACK.app
But It does ask where is iTunes when you connect the headset. At least after moving the window around, it doesn't nag me anymore.