A little research revealed the following helpful command
/System/Library/CoreServices/"Menu Extras"/User.menu/Contents/Resources/CGSession -suspend
Paste into an Automator workflow, save that (with file-type "application"), drag into the dock (and your application folder) - and you're all done!! You can even drag this to your finders' toolbar - cool!
(I know - there's an entry in the menu bar - but that's too hidden - and I needed a Quicksilver-enabled solution).