Automatic Uninstall - AVAST!

Tried to uninstall AVAST! using the provided Competitive Uninstall and the SEPPrep Tool.

But everytime I do that, AVAST! flashes itself on the screen, saying that an uninstallation is pending. Also, you have to type for a password before proceeding.

I use the default config file for SEP Prep Tool. So is there any way to customize it and uninstall AVAST! silently without flashing anything on the screen?

Thanks.