Instead of storing the values of custom fields in the tickets extra column, save them into their own table.
That way filtering tickets by custom fields can be done with a JOIN instead of a hackish LIKE on the extra column like so:
SELECT `tickets`.* FROM `tickets`
JOIN `custom_fields_values` AS `fields`
ON (`fields`.`custom_field_id` = 2 AND `fields`.`value` = "5.4.14" AND `fields`.`ticket_id` = `tickets`.`id`)