make the config smart base on environment

[eluser]newtonianb[/eluser]
I have several fields in config.php, database.php and constants.php that are different when i publish my site to server.
How can I make it smart and have it automatically pick the right one based on lets say hostname.


I tried if(strpos(base_url(),"localhost") === false)
but base_url() isn't working in these files, it actually seems to only work inside database.php

What else can I do?