Well, I figured it out. Here is the dcop commandline for reloading the bookmark.xml file in KDE desktop
so it can be used as a mouse menu:
dcop kdesktop KBookmarkManager-/home/username/.kde/share/apps/konqueror/bookmarks.xml notifyChanged ''
The above is all on one line, "/home/username" should be the path to your home directory, and the last item on the line is two single quotes, i.e. a quoted empty string which is needed so notifyChanged doesn't complain about a missing argument..