Using computer's proxy settings

Question

Currently I'm manually putting my local environment proxy settings in my settings.php file like so:

 $conf['proxy_server'] = '192....';
 $conf['proxy_port'] = ####;
 $conf['proxy_username'] = 'myusername';
 $conf['proxy_password'] = 'mypassword';
 $conf['proxy_user_agent'] = '';
 $conf['proxy_exceptions'] = array('127.0.0.1', 'localhost');

This works, but I work with a team, and the others on my team can see my login info when they enter the settings.php file. Plus when I change my password, I need to remember to change it here.

We're using Windows 7 machines. How could I make it so that Drupal automatically uses the logged-in user's credentials (like the way browsers seem to do) instead of hard-coding them into the settings.php file?