This is what I did with my BT Freedom Keychain GPS...
Turn on the GPS. Turn on BT, and search. Pair it (using the code provided - 0000 or 1234). Set up a comm port - I chose com8. Open the external GPS application - Start Settings System. Choose a free comm port (I used com0) in the Programs tab, then choose the BT comm port in the Hardware tab (com8 in my example). Under Access, check the box to allow sharing of the BT signal.
Go outside and turn on the GPS. Make sure BT is on, then go to GMM. Select Menu>Use GPS. You should see messages that GPS is initializing, number of sats used, and eventually see a flashing blue dot at your location. If that doesn't work, make sure that under the GPS settings in GMM you're using the first "automatic" setting. If you choose manually, you'll be conflicting with the external GPS app.