admin_page_demo.php

<?php
/**
 * Register an Admin Page - Example
 * 
 * NOTE: MU Plugin.
 * 
 * @author hakre <http://hakre.wordpress.com/>
 * @link http://wordpress.stackexchange.com/questions/1778/admin-config-screen-without-menu
 */

return AdminPageDemo::bootstrap();

class AdminPageDemo {
	static $identifier = 'adminpagedemo';
	/**
	 * plugin initialisation
	 */
	static function bootstrap() {
		//Admin Menu Hook
		add_action($hook = 'admin_menu', array(__CLASS__, $hook));
	}
	/**
	 * admin_menu action
	 */
	static function admin_menu() {
		$page_callback = array(__CLASS__, 'demo_page');
		$url = self::register_admin_page($page_callback);
	}
	/**
	 * Register a Callback as an Admin Page
	 * 
	 * This Page is not added to any menu.
	 * 
	 * @param Callback $callback
	 * @param String $identifier (optional)
	 * @return string URL for the new page
	 */
	static function register_admin_page($callback, $identifier = false) {
		//$identifier is optional.
		$identifier || $identifier = is_array($callback) ? $callback[1] : $callback;
		
		// Prefix Identifier
		$identifier = sprintf('%s_%s', self::$identifier, $identifier);
		
		// Wordpress Constant
		$parent_slug = 'options-general.php';
		
		// Get Hookname
		$hookname    = get_plugin_page_hookname( $identifier, $parent_slug);
		
		// Assign Callback to hook
		add_filter( $hookname, $callback );

		// Register Hook as a Page-Hook
		$GLOBALS['_registered_pages'][$hookname] = true;
		
		$url         = admin_url($parent_slug . '?page=' . $identifier);
		
		return $url;
	}
	static function demo_page() {
		echo 'This is your Demo Page.';
	}
}

#EOF;

thanks