installer.php

<?php
class plgInstallerSample extends JPlugin
{
	public function onInstallerBeforePackageDownload(&$url, &$headers)
	{
		$uri = JUri::getInstance($url);
		$uri->setVar('blahblah', 'blahblah');
		$uri->setVar('pid', 'xx');
		$uri->setVar('token', 'xxxxxx-xxxxxx-xxxxxx');
		$url = $uri->toString();

		return true;
	}
}