The genmon plugin does not execute a command on click when the corrresponding script needs root privileges. One can do that with a common desktop entry when opening a terminal with the action. This would be a nice feature for genmon too.
Use pkexec from Policykit to get a password dialog before the command will be executed. http://www.freedesktop.org/software/polkit/docs/0.105/pkexec.1.html
Mass-reassign all bugs from florian@ to goodies-dev@, thanks for the maintenance work! (and sorry for the bugmail spam..)
Raphael Groner is correct. You can use pkexec or gksudo to display a password dialog. Marking as WONTFIX.
There's also xfce4-polkit. https://github.com/ncopa/xfce-polkit