Reset DVD NAV system on a 2003 Prius?

I bought a used 2003 Prius and would like to do a total reset of the DVD nav system, essentially erasing all the waypoints, destintations, addresses, etc.

Does anyone know if there is a trick to do this? I've checked the FAQ's online and didn't notice anything.

Also, I asked a Toyota dealer and they said it could be done, but he didn't have the notes with the procedure available. Toyota corporate says it is not possible to reset the system. I have a hard time believing that the nav company creates a computer which cannot be reset.