Use a bluetooth headset JUST as a microphone?
You may be able to configure a bluetooth headset only as a microphone, but Rosetta Stone would refuse to recognize that microphone. a USB or an analog microphone is a must. It will NOT accept a bluetooth microphone but will accept the speaker part of the bluetooth headset. I tried to get the microphone to work with Rosetta Stone but no go. Here's the link as proof:
http://support.rosettastone.com/articles/en_US/Text/Will-my-headset-work-with-Rosetta-Stone/?q=Text&amp;l=en_US