1......i dont think you can....that would be a headset option/issue
2......so,while your bluetooth is connected,the gps sounds come through the heaset?
        i had the opposite happen.i wanted it in the headset and it was coming out of the speakers.
        now i have not used my gps for a long timeO(a couple firmware updates)something might have
        changed in one
3......i use handy shell.i has the bluetooth right on the home screen.
        two taps pf that takes me to the bluetooth  options,go tothe next tab right,then select headset you
        use/connect

        with out handy shell,touch the battery bar,it should bring up a box with the time and a symbol,
        touch the symbol/bluetooth/first tab right/select/connect


hope this helps