Here is a quick and dirty little trick I often use for faking environments in Wordpress installs for local development. The real trick here is just detecting whether or not a local config file exists and setting credentials appropriately.

local-config.php

<?php

// Settings used for local development
// do NOT track in your repository for deployment

/**
 * Following 2 lines overwrite the standard WP_HOME and WP_SITEURL in the
 * wp_options table of the database. Doesn't solve all problems, but any
 * URL's generated dynamically (You are using site_url('', 'relative'), aren't you?!)
 * will generate correctly.
 * 
 * Use http://wp-cli.org/commands/search-replace/ for anything else.
 * 
 */
 
define( 'WP_HOME',"http://localsite.dev"); // no trailing slash
define( 'WP_SITEURL',"http://localsite.dev"); // no trailing slash

// Debug settings
define( 'WP_DEBUG', true );
define( 'WP_DEBUG_LOG', true );

// Local DB credentials
define( 'DB_NAME', '' );
define( 'DB_USER', '' );
define( 'DB_PASSWORD', '' );
define( 'DB_HOST', 'localhost' );

wp-config.php

<?php

// Standard wp-config stuff here

/**
 * First condition tests whether or not a local-config.php file exists
 * which indicates we should be using the credentials specified in that
 * file. Handy for local development without altering production credentials.
 * 
 * WP_LOCAL_DEV is also defined which is handy if you need to add any debug code
 * anywhere in your theme.
 * 
 * If it doesn't exist, just carry on like you normally would in a wp-config.php file
 */

if ( file_exists( dirname( __FILE__ ) . '/local-config.php' ) ) {
	include( dirname( __FILE__ ) . '/local-config.php' );
	define( 'WP_LOCAL_DEV', true ); // We'll talk about this later
} else {
/** The name of the database for WordPress */
	define( 'DB_NAME', '' );
	define( 'DB_USER', '' );
	define( 'DB_PASSWORD', '' );
	define( 'DB_HOST', 'localhost' ); // Probably 'localhost'
	
	define('WP_DEBUG', false);
}

// Standard wp-config stuff here

Credit where credit is due... this comes from: Mark Jaquith
The original article elaborates on (and uses) the WP_LOCAL_DEV var created above. ("We'll talk about this later")