I have an iframe which does picture uploading to give a false sense of Ajax uploading.
<iframe style="border:none" src="someurl" width="100%" height="350px" id="iframe"></iframe>
$('#iframe_response', "#iframe").append('this should go there but it\'s not...');
Here's the answer! It's just a little confusing to start with but really easy!
Assuming that same origin policy is not a problem, you can use parent.document to access the elements, and manipulate them.
Hope this helps, Spent I fair bit of time figuring this out for you so I'd love the support of upping my answer!