I don't think it is possible peeps! The original project that creates the Menu was called 'GnoMenu' - they have rebranded it as ZorinMenu in 7. So you can now press Windows and Tab to get the Aero effect of windows stack but not the L Super which you can check in Preferences/Preferences but it will not work. The Zorin brothers are trying to keep things stable. I had an issue with this in 6 and got round it by removing gnomenu altogether and then installed gnomenu afresh following the guide on the upubuntu blog - search for upubuntublog/2012/03 and search for Menu in Ubuntu 12.04 - bear in mind 7 is based on 13.04 you COULD lose your Zorin DE!