how to do Currency conversion on Billing date in Bex query

Hi All,

My scenario is have to do currency conversion to USD from transaction currency at Bex level using Billing date .

For each records there will be one billing date based on that date conversion should be done .  this can be done in back-end using function module . but it should required at Bex level . could please share your inputs how it could be done .

Thanks in advance

Srinivas