How can I use this with express-proxy?

Hello,

I'm using express-proxy to proxy a form post to s3.
I want to add a field to the form. (The signed signature).

But I do not have a full node request. What I have is the buffer containing the multipart.

app.use('/proxy/s3', proxy('https://' + config.s3Bucket + '.s3.amazonaws.com', {
    decorateRequest: function(req) {
        console.log(req.bodyContent.toString());
        return req;
    }
}));

The req.bodyContent is the buffer that contains the multipart.

Is it possible for me to use this library or I have to manipulate the buffer manually.

Thank you very much!

==Edit==
I just read https://github.com/andrewrk/node-multiparty/blob/master/examples/s3.js
Maybe I should completely change my pattern. However, I am still interested in the original question. Can you manipulate multipart data before proxy it?

==Edit 2==
Just read detail of https://github.com/andrewrk/node-multiparty/blob/master/examples/s3.js#L45
Maybe this is not possible through proxy since the content length will not be correct.

Start by comparing the express-proxy example using req.bodyContent with multiparty's examples/s3.js, especially the referenced line about content length. Determine whether multiparty exposes an entry point for modifying multipart data before proxying. Done means documenting a supported approach or clearly recording that this proxy pattern is not supported.