copy the file /usr/share/kde4/services/plasma-runner-bookmarks.desktop to ~/.kde4/share/kde4/services/ (or ~/.kde/share/kde4/services/ depending on your distro)
then search for the line “X-KDE-PluginInfo-EnabledByDefault=true” and change this in
X-KDE-PluginInfo-EnabledByDefault=false
call “kbuildsycoca4 --noincremental” (I’m not sure if this is needed, but it can’t harm…)
After a logout/login (or reboot) the bookmark searching should be disabled in Kickoff.
And this will even survive system upgrades.