KDE combo-button delay feature - how to access from kbd?

http://usability.kde.org/activity/completed/combobuttondelay.php describes the combo-button delay feature. Anyone know how I can access the pull-down menu of such command buttons using the keyboard? A point in question is: the reboot button in the logout dialog has many boot options - I would like to select the option I want from this, using the keyboard only. (I can of course navigate to the button using Tab or cursor keys.) Thank you, Shriramana.