Thanks for this, it was just what I was needing. I was able to test out a solution for this that makes use of the htmlspecialchars() function in php. I have updated your webassist > email > templates > Blank.php file. Here is the updated copy of it.
All I did in this file is add in the htmlspecialchars function around the print out of the $pkey value. Please give this a try to see if it resolves this issue for you. In my test I was able to see the embed code in the email message.