Note that HHH-2697 is now fixed for Hibernate 4.1.3 You can now escape with backslash:
SELECT k.`news_master_id` AS id, @row \:= @row + 1 AS rownum
FROM keyword_news_list k
JOIN (SELECT @row \:= 0) r
WHERE k.`keyword_news_id` = :kid
ORDER BY k.`news_master_id` ASC