Ah, yes. I should have been clearer in my comment. Obviously, the request needs to be served from the domain or subdomain in question, but it doesn't need match

Ah, yes. I should have been clearer in my comment. Obviously, the request needs to be served from the domain or subdomain in question, but it doesn't need match the URL of the page you're on, and it doesn't need to be an iframe, nor be set by JavaScript. It can be a simple image request; doesn't need to be an iframe, and doesn't need to involve complex JavaScript. My point was that it doesn't need to require much complexity at all; just an HTTP request served by the domain in question that passes along the cookies that need to be served from the new domain.