com.apple.MCX.sidebar

I'm wondering if anyone has managed (har har) to get the com.apple.MCX.sidebar preference manifest to take effect? I'd like to put some common network locations in to users' sidebars and have it managed "often". However, it seems that no matter what I put in the "Custom URLs" attribute, nothing ever shows up in the sidebar. I've tried all sorts of variations, including straight paths like /Network/Foo, or file:///Network/Foo, or file:///localhost/Network/Foo. Has anyone had any success with this?