Custom post types and custom variables — add_rewrite_tag() question

function add_places_rewrite_tags() {
    add_rewrite_tag('%action%','([^&]+)');
}
add_action( 'init', 'add_places_rewrite_tags' );

First add the rewrite tag action (action=xxxx)

function add_places_rewrite_rules() {
    add_rewrite_rule('^area/([^/]*)/places/?','index.php?post_type=area&name=$matches[1]&action=places','top');
    add_rewrite_rule('^area/([^/]*)/([^/]*)/places/?','index.php?post_type=area&name=$matches[2]&action=places','top');
}
add_action( 'init', 'add_places_rewrite_rules' );

Then add a custom rewrite rule. (post_type=area may be different if you made a custom slug for the posttype, use the posttype name).

Remember to flush your rewrite rules to make this work (go to your permalink settings).