~/Library/LaunchAgents/local.job.screensaver.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	<key>Label</key>
	<string>local.job.screensaver</string>
	<key>LowPriorityBackgroundIO</key>
	<true/>
	<key>LowPriorityIO</key>
	<true/>
	<key>KeepAlive</key>
	<dict>
		<key>SuccessfulExit</key>
		<false/>
	</dict>
	<key>Nice</key>
	<integer>5</integer>
	<key>ProcessType</key>
	<string>Background</string>
	<key>ProgramArguments</key>
	<array>
		<string>/System/Library/Frameworks/ScreenSaver.framework/Resources/ScreenSaverEngine.app/Contents/MacOS/ScreenSaverEngine</string>
		<string>-background</string>
	</array>
	<key>RunAtLoad</key>
	<true/>
</dict>
</plist>