Setup a simple HTML redirect script
rename index.php then create index.html paste this in there
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<title>Redirecting you to the new control panel</title>
<meta http-equiv="REFRESH" content="0;url=http://stream.shellservers.net:2199/"></HEAD>
<body>
</body>
</html>
change stream.shellservers.net to your domain.. you could put a little message into the <body> tag saying that there has been an upgrade .. That will redirect almost instantly when they go the old url