Opposite of MySQL FIND_IN_SET
FIND_IN_SET returns the index of the match if it is found, and returns 0 if it is not found. Since 0 is FALSE you can just use NOT FIND_IN_SET('needle', 'haystack')
http://dev.mysql.com/doc/refman/5.0/en/string-functions.html#function_find-in-set
FIND_IN_SET('needle', haystack) = 0 should do the trick.