WordPress Post Voting – Vote once per IP on entire site

The only difference you need is the place where the IP address will be stored. Instead of a post meta use an option.

So, where the script says …

$voter_ips = get_post_meta($postid, "voter_ips", true);

… use …

$voter_ips = get_option( "wpse_59080_voter_ips", true );

… and where it updates a post meta you should update the option:

update_option( "wpse_59080_voter_ips", $voter_ips );