Their documentation says you can augment the tincan.xml file in the root like so :
<launch lang="und">http://my.lms.com/TCActivityProvider/story.html
?endpoint=http%3A%2F%2Fmy.lms.com%2Flrs%2Fendpoint%2F
&auth=OjFjMGY4NTYxNzUwOGI4YWY0NjFkNzU5MWUxMzE1ZGQ1
&actor=%7B%22name%22%3A%20%5B%22First%20Last%22%5D%2C%20%22mbox%22%3A%20%5B%22mailto%3Afirstlast%40mycompany.com%22%5D%7D
&activity_id=61XkSYC1ht2_course_id
®istration=760e3480-ba55-4991-94b0-01820dbd23a2
</launch>
And now the endpoint will go to your specified url. But no matter what I do, the URL never changes, and all the JSON statements are sent to the root of where story.html is located.