Set Storyline variables with javascript

Hi,

I know its possible to use java to set and get a variable in Storyline. I want to know if it can be taken a step further.

I have a membership site that user can subscribe to. I am using an iframe to embed a storyline course hosted on amazon S3. When a user opens a course module I want to use java to set a variable in storyline to equal their membership ID from the membersite. This way when they complete a quiz or select an option I can then use a trigger to execute a javascript (including a value for their membership ID) which makes an API call to my database updating their record with the response/pass/fail etc.

The issue I have is how to get the user ID which is in a hidden field on the webpage to be set as a variable in storyline.

Is this possible?

Thanks

Adam