Uploadifive and Amazon s3 - Origin is not allowed by Access-Control-Allow-Origin - amazon-s3

Question

I am trying to get Uploadifive (the HTML5 version of Uploadify) to work with Amazon S3. We already have Uploadify working, but a lost of our visitors use Safari without flash so we need Uploadifive as well.
I am looking to make a POST but the problem is that the pre-flight OPTIONS request that Uploadifive sends gets a "403 Origin is not allowed by Access-Control-Allow-Origin".
The CORS rules on Amazon are set to allow * origin, so I see no reason for Amazon to refuse the request (and note that it accepts the requests coming from Flash, although I don't know if Flash sends an OPTIONS request before the POST). If I haven't made some big mistake in my settings on Amazon I assume this has something to do with Uploadifive not being set up for cross-origin requests, but I can find no info on how to check/do this or even how to change the headers sent on the request.
Has anyone tried using Uploadifive with Amazon S3, and how have you gotten around this problem?
My S3 CORS setting:
<?xml version="1.0" encoding="UTF-8"?>
<CORSConfiguration xmlns="http://s3.amazonaws.com/doc/2006-03-01/">
<CORSRule>
<AllowedOrigin>*</AllowedOrigin>
<AllowedMethod>GET</AllowedMethod>
<MaxAgeSeconds>3000</MaxAgeSeconds>
<AllowedHeader>Authorization</AllowedHeader>
</CORSRule>
<CORSRule>
<AllowedOrigin>*</AllowedOrigin>
<AllowedMethod>POST</AllowedMethod>
</CORSRule>
Edit:
After testing Chrome with the --disable-web-security flag I stopped getting 403:s, so it does seem like it is Uploadifive that is not setting cross domain headers properly. The question has now become, how do you modify the cross domain settings of Uploadifive?

Answer 1

Victory!
After banging my head against the wall for a few hours I found two errors.
1) Any headers (beyond the most basic ones) that you want to send to Amazon must be specified in the CORS settings via the AllowedHeader tag. So I changed the POST part of my settings on Amazon to this:
<CORSRule>
<AllowedOrigin>*</AllowedOrigin>
<AllowedMethod>POST</AllowedMethod>
<AllowedHeader>*</AllowedHeader>
</CORSRule>
2) Uploadifive was adding the "file" field first in the formData, Amazon requires that it is the last field. So I modified the Uploadifive js to add the file field last. In 1.1.1 this was around line 393 and this is the change:
Before:
// Add the form data
formData.append(settings.fileObjName, file);
// Add the rest of the formData
for (var i in settings.formData) {
formData.append(i, settings.formData[i]);
}
After:
// Add the rest of the formData
for (var i in settings.formData) {
formData.append(i, settings.formData[i]);
}
// Add the form data
formData.append(settings.fileObjName, file);
This solved the issue for me. There might still be some work to do in order for Uploadify to understand the response, but the upload itself now works and returns a 201 Created as it should.