In the Windows Mobile 5.0 audio gateway implementation there are a couple of control codes to turn on audio routing through the bluetooth headset/handsfree device. I've only tried this with a couple of devices and had mixed (That's a really bad audio pun sorry!) results but here's a library to allow you to try it yourself. In theory it may work on some 2003 Second Edition devices too. I'd be interested to hear your feedback.

To set audio routing just call

InTheHand.Net.Handsfree.AudioGateway.RouteAudioToHandsfree = true;

And set to false to return to normal audio use.

Once fully tested and documented this will make it into the 32Feet package.