Multisite (wp-admin/network/sites.php) order by "spam"

I’m writing a plugin to display a sortable column on wp-admin/network/sites.php

<?php
/*
Plugin Name: MultiSite SpamColumn
*/

class MultiSiteSpamColumn{

	function init(){
		if(($_SERVER['PHP_SELF']=='/wp-admin/network/sites.php') && (is_super_admin())){
			add_filter( 'wpmu_blogs_columns', array('MultiSiteSpamColumn','register_column') );
			add_action( 'manage_sites_custom_column', array('MultiSiteSpamColumn','display_field'), 10, 2 );
			add_filter( 'manage_sites-network_sortable_columns', array('MultiSiteSpamColumn','register_sortable_column') );
		}
	}

	function register_column( $columns ) {
		$columns[ 'spam' ] = __( 'Spam' );
		return $columns;
	}

	function display_field( $column, $blogid ) {
		if ( $column == 'spam' ) {
			echo get_blog_status( $blogid, 'spam');
		}
	}

	function register_sortable_column( $columns ) {
		$columns[ 'spam' ] = 'spam';
		return $columns;
	}

}
add_filter( 'init' , array('MultiSiteSpamColumn','init') );
?>

The sortable field finaly shows up, however results are not sorted yet.
I’ve tried the query, posts_orderby and posts_clauses filters to modify the query but can’t get it to work.

A temporary solution I found to make it work is by using a core-hack in wp-admin/includes/class-wp-ms-sites-list-table.php around line 82:

$order_by = isset( $_REQUEST['orderby'] ) ? $_REQUEST['orderby'] : '';
		if ( $order_by == 'registered' ) {
			$query .= ' ORDER BY registered ';
		} elseif ( $order_by == 'lastupdated' ) {
			$query .= ' ORDER BY last_updated ';
		} elseif ( $order_by == 'blogname' ) {
			if ( is_subdomain_install() )
				$query .= ' ORDER BY domain ';
			else
				$query .= ' ORDER BY path ';
		} elseif ( $order_by == 'blog_id' ) {
			$query .= ' ORDER BY blog_id ';

//begin hack

		} elseif ( $order_by == 'spam' ) {
			$query .= ' ORDER BY spam ';
//end hack

		} else {
			$order_by = null;
		}

Any help is appreciated to play safe on future-updates, thanks.