Gravity Forms Dynamic Population

Ok im a little confused on exactly what your trying to do.

If i got it right you have possibley dozens of links with that class and a single form you want to populate.

The form is loaded already when the page loads so clicking the link will show the form but by default nothing else happens.

You can override this functionality with a little custom js function like http://ww.wp.xz.cn/support/topic/open-an-iframe-inside-a-modal-box?replies=5#post-4651875.

In your case maybe instead of changing the iframe src attribute you change the value of a form field based on the ?subject parameter.