Add an action that would check if remote computers are waiting for reboot or not. Optionally it would be possible to use same approach in "Restart computer" action that would only run if computer is in fact "reboot pending" state.
This registry value could be used to identify those:
http://technet.microsoft.com/en-us/library/cc960241.aspx
This registry value could be used to identify those:
http://technet.microsoft.com/en-us/library/cc960241.aspx