Redirect the "Access denied…" to my 404 page?

Does anyone know how to change the “Access denied” message to a 404 page instead?

when someone (other than admin) tries to access dashboard?
I want to change:

Access Denied. Your site administrator has blocked your access to the WordPress back-office.

to my 404.php page.

the code for that message is:

* Block user access to admin panel for specific roles
     *
     * @global string $pagenow
     */
    function block_admin_access() {
        global $pagenow;

        $access_level = wpuf_get_option( 'admin_access' );
        $valid_pages = array('admin-ajax.php', 'async-upload.php', 'media-upload.php');

        if ( !current_user_can( $access_level ) && !in_array( $pagenow, $valid_pages ) ) {
            wp_die( __( 'Access Denied. Your site administrator has blocked your access to the WordPress back-office.', 'wpuf' ) );
        }
    }

Thanks everyone

http://wordpress.org/extend/plugins/wp-user-frontend/