P42101 - Retrieve Freight code (FRTH) at Grid from Header Cache

In P42101 Order entry the Freight code is entered using Sub Form - P421001.  I need to create a logic for using this FRTH value from header and use it during order detail process for each grid line (P421002).  But at grid level we don,t have the value of F4201.FRTH.  How can we have access or retrieve.  Is there a business function I can use to retrieve it from Header cache.  I tried to retrieve using the session key and related keys and BSFN B4210610 - SO Header View Controller. But the value of Freight code is not retrieved.