Change audio device automatically when connecting HDMI cable? How?

I bought a laptop with a HDMI connection to make things easier for me when
I'm watching movies on the TV.
When I connect the HDMI cable to the TV Vista detects it and automatically
extends the desktop to the TV just like I want it to. The sound however is
still coming from the speakers on the laptop until I change the default audio
device manually in the audio properties (it's realtek HD Audio by the way).
Is there any way to make Vista understand that also the audio output should
be switched to HDMI automatically whenever I connect the cable? If not, how
do I go about making some kind of executable or regfile that I just can
doubleclick when I want to use HDMI for sound and vice versa?

Thanks in advance!