Screenpop populating a textbox

Version 1
    This document was generated from CDN thread

    Created by: Faisal Zaidi on 14-05-2013 09:57:21 AM
    I have a screenpop where i need to populate a textbox with the value of a CallVar (or any text as in the example below). i have based the screenpop gadget on the sample provided with the iframe pointing to a very simple form but I can not seem to populate the textbox within the iframe, I belive the JS code should be as follows (usually in the onload function of the html page - works in a standalone html page) but im not sure where/if this is fit for purpose within a gadget?
    var ifrm = document.getElementById('iframeid');
    var innerDoc = ifrm.contentDocument || iframe.contentWindow.document;
    var textBox = innerDoc.getElementById('idCallVar10');
    textBox.innerText = "hello!";

    Subject: RE: New Message from Faisal Zaidi in Finesse - Tips and Tricks: Screenpop p
    Replied by: David Lender on 14-05-2013 10:25:22 AM
    My understanding is you have to use cross document messaging in order to access the page within the iframe.
    https://en.wikipedia.org/wiki/Cross-document_messaging

    Subject: RE: New Message from Faisal Zaidi in Finesse - Tips and Tricks: Screenpop p
    Replied by: Faisal Zaidi on 15-05-2013 04:12:06 AM
    this looks like it may work but isnt an option as it requires coding in the destination (popup) page. Any alternatives? perhaps by not using an iframe? i'm all out of ideas...