Don't know if this will help, but I've got here a single user machine that lets a normal user, xparrot, to halt and reboot the computer without password. My /etc/sudoers has a line:
xparrot ALL = (ALL) NOPASSWD: /sbin/halt, /sbin/reboot
And my ~/.bash_profile has these lines:
alias halt="sudo /sbin/halt"
alias reboot="sudo /sbin/reboot"