Ability for payment processors to store additional data about financial transactions

I'm developing a payment processor for Realex, however, I would like to be able to store more information that the current financial_trxn table can hole. For example, Realex batch their transactions by the day, and they assign a batch_id to each of these batches. It would be really useful to be able to store this batch id to help locate transactions,

They also pass back a message and an auth_code, which may also be useful in locating transactions at a later date. Again, it would be nice if there was a place to stopre these. Perhaps an additional database column that could be used to store additional data that may be unique to each payment processor, in a serialized form perhaps?