send xml with wwwform for youtube video upload from unity

How do I send xml with a wwwform post? The xml would be generated as a string in the script. would it be considered binary data using wwwform.addBinaryData(). If so how would I get a string to be binary data.

I'm trying to upload a video to youtube and it requires post parameters and some xml to be sent at the same time. Here's a short refererence.

https://developers.google.com/youtube/2.0/developers_guide_protocol_browser_based_uploading

Thanks,

Dan