Create a "Software Release" just like you do for a Windows application.
Click "Add package" in the "Software Release" window and add "Office2011-1401UpdateEN.dmg ", make sure you select the Office2011-1401UpdateEN.dmg file and click "Set Installation File"
Click "Add command", select "Installation file type:" = "DMG Software Installation File", select "Command type:" = "Install", click the "Edit" button, select "Installation File:" = "Office2011-1401UpdateEN.dmg", click "Generate Command Line", click "OK"
You should now have a Command line:
pkg-rollout -f 'Office2011-1401UpdateEN.dmg'