Bypass Maintenance Mode in Magento with custom HTTP_USER_AGENT

index.php

Overwrite the maintenance change in index.php file conditional with the follow, using a more unique User Agent is recommended.  
Chrome/Firefox/etc. most browsers offer means via extensions or development tools to set a customer User Agent.  Utliziing this
you can bypass the maintance mode for Testing when you don't have a Static IP:

# If user agent is "QA" bypass maintenance mode (customize user agent for more uniqueness)
if (file_exists($maintenanceFile) && $_SERVER['HTTP_USER_AGENT'] != "QA") {
    include_once dirname(__FILE__) . '/errors/503.php';
    exit;
}