TYPO3: Use an extension within an Extension

// add compatibility for other extensions
// for use in extensions: insert a marker with this object.
$extensionParams = array (
    'includeLibs' => 'typo3conf/ext/extension/pi1/class.tx_extension_pi1.php',
    'userFunc' => 'tx_extension_pi1->main',
    'otherConfigurationForPi1' => 'blaat',
);

$extension = $this->cObj->USER($extensionParams, 'USER');