1) you would need another set session code block:
<?php
if (!session_id()) session_start();
if($_SERVER["REQUEST_METHOD"] == "POST") {
$_SESSION["updFile2"] = $WA_DFP_UploadStatus["WA_UploadResult2"]["serverFileName"];
}
?>
and another link:
<a href="http://www.mydomain.com/uploads/<?php echo $_SESSION['updFile2']; ?>">click here for second image</a>
2) maybe unset the session at the bottom of the page using this code after the </html> tag:
<?php
if(isset($_SESSION["updFile"])) unset($_SESSION["updFile"]);
if(isset($_SESSION["updFile2"])) unset($_SESSION["updFile2"]);
?>