Reversing Documents in FI

The FB08 transaction reverses the documents in the FI but has a drawback that it takes into accout the exchange rate on the posting date of the original document and not on the reversal date.

However we required a functionality that post with the rate on reversal date.

I am developing a program which creates a new document with reference to another document which would be considered as reversal( eg 100 is original document and 101 new document is considered as reveresal document)

this is working fine.

however if the user tries to reverse 100 it is creating 102 and if he tries to reverse 101 it is creating 103.

How can i fix this issue.