Exits in FI

hello ,

Enhancement Technique: How to Use Substitutions

https://www.sdn.sap.com/irj/sdn/go/portal/prtroot/docs/library/uuid/707439da-ead9-2910-5c97-af6ca0b6fbb1

FI Enhancement Technique – How-To-Guide on the Usage of Business Transaction Events (BTE)

https://www.sdn.sap.com/irj/sdn/go/portal/prtroot/docs/library/uuid/207835fb-0a01-0010-34b4-fef1240ba9b7

i went through above links....i have a similar requirement.. i want to populate business area(GSBER) field based on GL account, while posting(in line items)... but in both the cases business area not found in substitutable fields.... how can i populate business area field thats not in substitutable field ? please help me...

Regards,

Maya