In the past weeks Konstantinos Smanis has been working in adding Grub2 and Burg submenu support in kdm and in the shutdown dialog. He had implement the support for the C++ version of the dialog used until KDE SC 4.8.x. However, since KDE SC 4.9 now uses QML based shutdown dialog I had to add some changes in it to support submenus as well. Here is result:
This will work out of the box in KDE SC 4.9.1 along with fixes for menus not reacting to clicks problem.