activate-plugins-by-stage.php

<?php
add_filter( 'option_active_plugins', 'activate_local_plugins' );
/**
 * Add our local plugins to the list of active plugins.
 */
function activate_local_plugins( $plugins ) {
	if ( defined( 'WP_STAGE' ) && 'local' == WP_STAGE ) {
		$local_plugins = array(
			'wordpress-beta-tester/wp-beta-tester.php',
			'wordpress-importer/wordpress-importer.php',
		);
		foreach ( $local_plugins as $plugin ) {
			$plugins[] = $plugin;
		}
	}
	return $plugins;
}