Well, no one could find the answer for me- even the Symantec support and engineers that I spoke with. So I had to figure it out myself. It seems that the only way to get the portal to re-prompt for installation is to unregister the launcher.dll located in "C:\Windows\Downloaded Program Files\". I have acreated a simple .bat file to do this for users that run into this problem. As soon as they revisit the site it will prompt them to install the agent. Gee, that was easy.
By the way, it seems that your streaming portal must be added to compatibility view in Internet Explorer 11 for the install to kick off correctly. Good luck!