The web viewer as a general statement your web browser in FileMaker. Much like your browser, you would have to take a look at the site's HTML and see if its even possible to skip all of that.
If you look here:
I believe that you are trying to go against their policy. Perhaps you can contact them and see if they have a advertisement free link service which usually come with a price.
That being said, they have built in session security to stop you anyway.