Needs Diff. Exchange rates type for sales trans and Purc Trans

Hi Gurus,

My requirement is that for a same foreign currency i need to pick two different rates one for purchase related activites and another for sales related activites. is that possible in standard SAP.

Example of my scenario:

My company code currency is INR.

on 10.09.2007 if i make purchase of goods in USD system picks the rate i maintain for usd from the exchange rate type "M".

On the same day if i make any sales in USD system is picking it again from the same exchange rate type "M', but i want to pick it from exchange rate type "G".

Kindly Advice me what to be done.

Thanks and Regards

Karthik