How to create a parse rule set that will calculate inverse exchange rate using 'payment amount' and

Summary

Is there a way to create parse rule set which will calculate inverse exchange rate using 'payment amount' and 'Original Amount' (like using formula payment amount/original Amount)?

Content

When in case of foreign/cross-currency payments (eg: SEK payment from GPB account), the bank statement (BAI) file has Payment amount,  
Original Amount, Currency and exchange rate.

unfortunately, the exchange rate on the BAI file is GPB -> SEK instead of  SEK ->GPB. This is causing the wrong exchange rate gain or loss calculation in Oracle.

Bank is unable to provide the inverse exchange rate on the BAI file.