I'm not, but that doesn't work. I've tried. The menu I'm talking about is the one that you see when the KDE login screen comes up.
The button reads "Menu" and you click on it, and some submenus come up.
One of these says "Session type" and gives a list of various window managers, and allows you to pick the one you'd like to use for this session. No matter which of those in the list I pick, KDE always starts.