In Vista, how to redirect audio-in, audio-out to specific microphone and speakers instead of the default ones?

Hi all,
My app provides a combo-box with the list of endpoint audio devices.
When user selects an endpoint audio device (e.g. a speakers and a
MIC), my app has to use those selected devices for audio-in and audio-
out. Please show me how to make that work on Vista. When I ran my app
on a Vista PC which has 2 headsets: one USB and one regular headset.
Vista OS automatically selects the USB headset as the default
endpoint audio device. Regardless which other device I selects, all
audio-in and audio-out still come in and go out thru the USB headset.
This is not what my app wants to offer. I see that the
IMMDeviceEnumerator interface of Vista has a
GetDefaultAudioEndpoint(), but no SetDefaultAudioEndpoint(). Is there
anyway I can programmatically redirect audio-in and audio-out to a
specific endpoint audio device instead of the default one?

Thanks very much for any hints, suggestions, samples, and advices you
can provide.

vistaheadache

.