jquery – 如何避免文件上传时的CORS预检请求？

<input type='file' name='file' class='cloudinary-fileupload' 
  data-url='https://api.cloudinary.com/v1_1/wya/auto/upload' />
<script>
  $('.cloudinary-fileupload').fileupload();
</script>

由于它是外部目标,因此浏览器会发起CORS请求.但是,我注意到浏览器会预先设置CORS预检请求.
http://www.html5rocks.com/en/tutorials/cors/提供了关于何时触发预检请求以及何时未触发预检请求的非常好的见解.据我所知,我的请求符合CORS简单请求的所有标准(参见第‘Types of CORS requests’节).

发送到外部服务的文件上载请求：

POST /v1_1/wya/image/upload http/1.1
Host: api.cloudinary.com
Connection: keep-alive
Content-Length: 22214
Accept: */*
Origin: http://wya.herokuapp.com
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_1) AppleWebKit/537.36 (KHTML,like Gecko) Chrome/32.0.1700.107 Safari/537.36
Content-Type: multipart/form-data; boundary=----WebKitFormBoundarym73rCIa6t8eTNkTa
Referer: http://wya.herokuapp.com/
Accept-Encoding: gzip,deflate,sdch
Accept-Language: sv-SE,sv;q=0.8,en-US;q=0.6,en;q=0.4,de;q=0.2

在文件上载请求之前发送到外部服务的附加预检请求：

OPTIONS /v1_1/wya/image/upload http/1.1
Host: api.cloudinary.com
Connection: keep-alive
Access-Control-request-Method: POST
Origin: http://wya.herokuapp.com
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_1) AppleWebKit/537.36 (KHTML,like Gecko) Chrome/32.0.1700.107 Safari/537.36
Access-Control-request-Headers: accept,content-type
Accept: */*
Referer: http://wya.herokuapp.com/
Accept-Encoding: gzip,de;q=0.2

有没有办法避免这个额外的预检请求？据我所知,文件上传请求是一个CORS简单请求,因为它是带有Content-Type multipart / form-data的http POST,只有简单的请求http头.

我想摆脱额外的预检请求的原因是Cloudinary发送http 302/304重定向作为对文件上传的响应.浏览器不遵循这些重定向. Chrome失败并显示以下消息：

XMLhttprequest cAnnot load https://api.cloudinary.com/v1_1/wya/image/upload. 
The request was redirected to 'http://wya.herokuapp.com/upload?bytes=21534&created_at=2014-02-12T09%3A04%3…d5b62ebb92b9236e5be6d472df242d016&type=upload&version=1392195882&width=723',which is disallowed for cross-origin requests that require preflight.