How to set basic auth headers for file upload in adobe AIR?

Question

I have an AIR application that uses basic auth to talk with my server. All of my "normal" requests work great, but file uploads are not sending my basic auth headers.

var file = new air.File();
//config file selection here...
file.upload(new air.URLRequest('http://mycompany.com'), 'data');

I'm using the URLRequestDefaults.setLoginCredentialsForHost method to initialize basic auth headers for all of my regular requests, but according to Adobe documentation for the FileReference.upload method, "custom HTTP request headers are not supported".

How else can this be accomplished?