Same Installation folder for different sites (config.php and database.php)

You can check what subdomain ist active and then make a switch in the config.php and database.php
Somthing like this quick an dirty snippet

PHP Code:

$subdomain = explode('.', $_SERVER['HTTP_HOST']);
if ($subdomain[0] != 'www' && count($subdomain) == 3)
{
    if ($subdomain[0] == 'zone1')
    {

    }
    //etc.
}
else
{
    // no subdomain
}