compare actual to budget in foreign currency

Hi,

My client budgetary control (absolute)  for PO and invoice. Problem arise in foreign currency transaction: during PO process, it has already pass the budgetary control. But, the invoice is put on hold with insufficient fund because of the fluctuation in exchange rate and oracle check the budget in functional currency, not in original currency amount.

Is there any way to make Oracle check the budget in original currency amount, not converted to functional amount?

Thanks,

Arie