// No need to trigger WordPress search since Google Custom Search is being used
function cf_kill_wp_search( $where, $query ) {
    if( ! is_admin() && $query->is_search() )
        $where = ' AND 1=0';

    // Only need to do this for the main query
    remove_filter( 'posts_where', 'cf_kill_wp_search', 10 );

    return $where;
}

add_filter( 'posts_where', 'cf_kill_wp_search, 10, 2 );