gistfile1.php

<?php

$using_ssl = isset($_SERVER['HTTPS']) && $_SERVER['HTTPS'] == 'on' || $_SERVER['SERVER_PORT'] == 443;
add_action('wp', 'check_ssl');
function check_ssl()
{
    $page_id = 2;// Page ID 2 must be https
    if (is_page($page_id) && !$using_ssl)
    {
        header('HTTP/1.1 301 Moved Permanently');
        header('Location: https://' . $_SERVER['SERVER_NAME'].$_SERVER['REQUEST_URI']);
        exit;
    }
    // All other pages must not be https
    else if (!is_page($page_id) && $using_ssl)
    {
        header('Location: http://' . $_SERVER['SERVER_NAME'].$_SERVER['REQUEST_URI']);
        exit;
    }
}

?>