[otrs] Define different freetext field for differens queues?

Dear all, Currently our OTRS uses freetext fields to define the type of category (Tech, Billing, General, ...) Since we have different queues for all our product, it would be desirable if we could have specific freetext fields for every queue. For example one of our product has no billing support, so it is senseless to have the "billing" freetextfield available here. Any help or hints are welcome! Thanks, Sebastian