How to use pre-persisted values from Inbound XML to configure a business number rule in OTM/GTM?

Summary:

We are trying to configure a scenario in GTM where GTM is expected to generate a sequence number for every Trade Transaction based on the XML value flowing from Fusion. We have an Inbound integration from Fusion to GTM using OIC as a middleware where Trade Transaction details will be sent from Fusion which will have Certain Fusion business process Id's and once transaction gets created in GTM it should use those values dynamically and generate a unique sequence.

For Example: Inbound XML has a refnum qualifier as Order Owner and the value of this qualifier should be used in the Trade Transaction ID.