for the impatient followers of me reading this:
in a temp directory somewhere (replace the .deb file with yours):
dpkg-deb -X /var/cache/apt/archives/kdebase-data_4%3a3.5.5a.dfsg.1-2_all.deb .
cp ./etc/xdg/applications-merged/kde-essential.menu /etc/xdg/menus/applications-merged/
and just to make sure:
cp ./etc/xdg/applications-merged/kde-essential.menu /etc/xdg/menus/kde-applications-merged/