The RadUpload control uses the standard input type='file' element and the upload is handled by the ASP.NET framework. We only find the uploaded file from the submitted form and provide an API layer over it. When a file is uploaded it is stored and handled by the framework, a process which is black box for us. To overcome this problem you should send the file on chunks which the RadAsyncUpload does(2MB each).
Check out the Telerik Platform - the only platform that combines a rich set of UI tools with powerful cloud services to develop web, hybrid and native mobile apps.