Mageno: Create Empty Template.

In your controller action issued this command.

$this->loadLayout(false); // Issue this to disable loading of your layout
$this->getResponse()->setHeader('Content-Type','text/xml'); // Set this depending on you file content type

/**
* .... Put you other code here
*/
$this->renderLayout(); // Finally render your layout

For complete details see also the source Custom controller actions result in blank template