No exchange rate difference to be posted between GR and IR

Hello,

I need to set up the following scenario for a purchasing flow in foreign currency.

Local currency = EUR, foreign currency = USD

Material valuated at MAP

PO value = 1000 USD

Good receipt day 1, exchange rate M on that day : 1 USD = 0.8 EUR

Debit Inventory 1000 USD 800 EUR

Credit GR/IR 1000 USD 800 EUR

Invoice receipt day 2, exchange rate M on that day : 1 USD = 1 EUR

SAP as standard does the following (alternative logic, see http://help.sap.com/saphelp_erp60_sp/helpdata/en/45/5c4a52eedd2f95e10000000a155369/content.htm) :

Debit GR/IR 1000 USD 800 EUR

Credit Vendor 1000 USD 1000 EUR

Debit unrealized FX diff 0 USD 200 EUR

We don't want this, we want the following posting :

Debit GR/IR 1000 USD 800 EUR

Credit Vendor 1000 USD 800 EUR

Meaning that the IR picks up the fx rate from the GR and no fx diff posting is generated.

Fx diff will only be posted when the vendor is paid.

I know it's possible to enter an exchange rate manually in MIRO , but is there a way to automate this ?

Thanks for your insight,

Rom