Non-standard delivery integration interface(Custom delivery IDoc--> PI --> TM)

My assumption is that our PI resource will map incoming fields to the service(IntracompanyTransportationRequestRequest_In) and create DTR in TM.

The inbound 940 also has large amount "extra fields" that is not required but management is keen on saving this data in TM for later use.

What would be the best approach to take here?

My current approach is to :

1. Enhance the service(IntracompanyTransportationRequestRequest_In) in TM to allow for these extra fields to created. Once PI calls this service, use the BADI for this service to get the extra fields and save it 'somewhere'. Maybe I will also need to enhance the business object for DTR(create a new node) to hold these extra fields? Is my idea a valid approach?

thanks