The only Bluetooth interface that will work with the factory Bose system is the one supplied on bluetooth models. To retrofit, you would have to add the parts, ie bluetooth module, mic, steering wheel controls, etc from Nissan. Definitely not cheap or easy.
If all you want is a handsfree speakerphone and voice activated dialing, then look for a standalone device. My wife has a Blueant Supertooth Light.
http://myblueant.com/supertoot...e.htm. It clips to the sunvisor and give her a handsfree speakerphone. There is also the Supertooth 3 which adds voice activated dialing.
http://myblueant.com/s3_handsfree.htm
Parrot makes similar systems:
http://www.parrot.com/usa
Good luck and kudos for wanting a handsfree... keep both hands on the wheel and eyes on the road!