Display TOS / Official Rules in Lightbox / Modal

Hello,
I'm hoping to create a TOS / Official Rules style button (a la http://wpsmith.net/2011/plugins/how-to-create-a-custom-form-field-in-gravity-forms-with-a-terms-of-service-form-field-example/ ), but hoping to have a link to show it in a lightbox / modal.

It's possible that I won't need the whole custom form field, as I'm thinking I could just use an HTML box with the following:

<div class="rules">
        <a href="#" class="lightbox-activator">Read the rules</a>
 </div>

But it would be great to use the input in one of the boxes on the form as a merge tag to help generate a custom link (href). But that doesn't seem to get passed into the HTML code box.

<div class="rules">
        <a href="{Field Name:{field_id}}" class="lightbox-activator">Read the rules</a>
 </div>

Can someone point me in the right direction or do you have some snippets?