Got it! :)
The answer is: typo3conf/AdditionalConfiguration.php
if this file exists it's included automatically, to overwrite some values we need to use well-known syntax ie.:
<?php
$GLOBALS['TYPO3_CONF_VARS']['DB']['database'] = 'my_local_database';
$GLOBALS['TYPO3_CONF_VARS']['DB']['host'] = 'localhost';
$GLOBALS['TYPO3_CONF_VARS']['DB']['username'] = 'username';
$GLOBALS['TYPO3_CONF_VARS']['DB']['password'] = 'mypassword';
?>
From "What's new" SlideShare (page 33)