Launch the OS X Screensaver From The Dock
Here is how to start the screensaver from an icon:
- Open a Finder Window
- Navigate to the following area: /System/Library/Frameworks/ScreenSaver.framework/Versions/A/Resources/
- Drag ScreenSaverEngine.app to the dock or desktop
- Click the created icon to start the screensaver
From: http://www.tech-recipes.com/rx/2132/os_x_activate_screensaver_dock_icon/