Payment of Foreign Currency Invoices with User exchange rate

We have multiple foreign currency invoices which needs to be paid by ‘User’ defined exchange rate on the invoice.

Examples as below

1. Invoice 1 booked on 01-Aug-18 with exchange rate @ 0.86698 (1 Euro = GBP)
2. Invoice 2 booked on 10-Aug-18 with exchange rate @ 0.91120 (1 Euro = GBP)
3. Invoice 3 booked 20-Aug-18 with exchange rate @ 0.88775 (1 Euro = GBP)

Now we want to pay all these invoices via Single Payment Batch (PPR) on 20-Sep-2018 based on the exchange rate entered at time of invoice booking i.e.

Invoice 1 to be paid @ 0.86698 (1 Euro = GBP); Invoice 2 @ 0.91120 (1 Euro = GBP) and Invoice 3 @ 0.88775 (1 Euro = GBP).

Currently, payment process request only allow single exchange rate per payment process. We don't want to pay all these invoices by average exchange rate and adjust against realized gain & loss account.