In a multi-user environment the option should be available when KDE4 is installed. All we need are some desktop files in tdebase/tdm/kfrontend/sessions. We need only copy the files from KDE4:
/usr/share/apps/kdm/sessions/kde-plasma-safe.desktop /usr/share/apps/kdm/sessions/kde-plasma.desktop
I tested adding the files on a system with KDE4 installed and another without. With the former the options appeared as expected and with the latter the options did not appear as expected.
Comments?
Darrell