dbusmenu provides a facility for global menus, it's developed by Canonical for Ubuntu but freely available for other OS's. Gtk and Qt support it, but LibreOffice will need an additional patch to do so. A quick review of LibreOffice menus suggests it doesn't use anything that is not already provided by dbusmenu, it should simply be a matter of connecting the dots. Am filing this bug here to facilitate coordination of a fix, as the issue has been reported in the Ubuntu bugtracker.
Mark: Thank you for the report! Marking it as 'EasyHack' [though it is going to be an 'Advanced Hack' I am afraid ;-)] to be accessible from http://wiki.documentfoundation.org/Development/Easy_Hacks
Work has begun on launchpad by http://launchpad.net/~alberto.ruiz to achieve this. See Bug 664731: https://bugs.launchpad.net/bugs/664731 And bzr Branch: https://code.launchpad.net/~lo-menubar-team/lo-menubar/trunk
initial import of lomenubar with: http://cgit.freedesktop.org/libreoffice/libs-core/commit/?id=ec176090c881c6d6b85606c6711ed621c5af7531
Alberto: Should I reassign to myself?
Deteted "Easyhack" from summary
Rebased and merged to master at https://gerrit.libreoffice.org/gitweb?p=core.git;a=commit;h=349fa28a5998d10b110da1a7fcc6b5b24d5940b1
Migrating Whiteboard tags to Keywords: (EasyHack TopicUi) [NinjaEdit]