Need to set document.domain for Ajax-enabled submissions

I am running a site (www.example.com) that uses iframes from a subdomain (test.example.com).

In order to communicate between them (due to same-origin policy) I need to set the JavaScript variable document.domain = 'example.com' . This is all fine and works great.

However, when Gravity Forms in introduced, the Ajax-enabled submissions fail (because presumably the Ajax code returned that gets loaded into the hidden GF iframe expects the standard http://www.example.com)

Sadly, browsers do NOT let you reset the document domain back to the original, once you have set it to the superdomain.

Long story short: I need to be able to insert the document.domain code into the HTML returned by the Ajax submission of a form. I don't see a JavaScript hook for such a thing. Is there a way to do this via a PHP hook?

I know I can just turn Ajax off and it'll work, but that's not an elegant solution.

Any advice would really be appreciated! Thanks.

I'll see if the dev team has any ideas for you here.