Currency Conversion rate need to be defined in shipping

Hai

Any option available to define currency conversion rate in shipping transaction (before ship confirm).
Our business is sales order booked for bulk quantity once in a month and shipping made for partially.
day to day the coversion rates are changed,we need to define currency conversion rate at the time of
shipping.

Note - Now we are used the below said options.

User Specified Rate - user need to enter the conversion rate and date in sales order header while creating the sales order.
Corporate Exchange Rate - day wise rate are defined in 'Daily Rates' form.

Regards,
Shiva.