Exchange rate difference in J1iin and VF01

Dear Gurus,

I am facing an export scenario issue where a commercial invoice(VF01) is created 15 days before the excise invoice ( J1IIN) . In Between this time difference the exchange rate has changed. So in commercial invoice we are getting the old exchange and rate and in excise invoice new exchange rate for USD is picked.

Can you please help me find how to make sure that the excise invoice (J1IIN) picks the same exchange rate that comes in VF01 doc.

Thanks in advance,

Rohit