Problem with OM transaction type for IR/ISO and consignment orders

We have a separate OM transaction type for IR/ISO's and consignment order flows. As both would start with creation of Internal Requisitions geting converted in to either ISO's or consignment orders. As per the standard application setup's in purchasing options, we can either assign ISO transaction type or Consignmen transaction type when an IR gets converted to ISO or consignment order. We need to have separate transaction types to track these two types of orders. Based on this limitation, we are unable to have different transaction type for these two order flows.

Any pointers on how we can default a specific transaction type on type of requisition (Internal) is appreciated.