i am sorry. i read a bit fast the first post. my suggestion works fine for "ctrl-alt-del" combination. i wrote a script at home. i will check later and let you know if it is necessary.
if you want to setup the commands, like you wrote in your first post, i suggest a look here
there is everything that you need.
i suggest also read more the threads here before adding users in sudoers to shutdown without root password. it can be a serious security issue if you are running a server.