Vista - WMP sound to multiple playback devices

I have two playback devices that show up in the Vista's new Volume Mixer.
One is my speakers and the other is my LineX FM transmitter device. Windows
Media Player uses whichever device is selected as the default playback
device. Is it possible to have WMP output to multiple playback devices? If
not, is it possible to select which output device WMP uses without having to
shutdown WMP, change the default output device, and then restart WMP?

This applies to other applications as well, but I'm primarily trying to get
this working with WMP. The new Volume Mixer is great in that it allows per
application volume/mute control, but it seems as though it should allow the
applications to be assigned to individual playback devices as well.

Thanks,
Yogi