Does your site make use of a dedicated SSL certificate, is the https domain the same? If so then you could make use of some php to do this form you. If you add the following code to the top of any pages that you would like to automatically redirect to the https version it will redirect the user.
<?php if((!(isset($_SERVER['HTTPS']))) || ($_SERVER['HTTPS'] == "") || ($_SERVER['HTTPS'] == "off"))header("Location: https://" . $_SERVER['HTTP_HOST'] . $_SERVER['PHP_SELF']); ?>