Accessing server-variables in callback functions

I'm using server-side processing, using a modified version of the sample PHP code from this site; that code responds with this:

$output = array(
		"sEcho" => intval($_GET['sEcho']),
		"iTotalRecords" => $iTotal,
		"iTotalDisplayRecords" => $iFilteredTotal,
		"aaData" => array()
);

What I'm completely stuck on is I know that in certain callback functions, like fnFooterCallback, I can access aaData.

What I'm trying to do is, in the server response, I have another variable that contains a value and I need to access it in javascript, in one of the callback functions (on fnDraw, footer or header callbacks). Is there a way I can get access to the whole json response so I can grab the value of iTotalRecords or any other variable, and not just aaData?