Once all your transactions (timesheets, WIP, expenses, travel, disbursements) are finalized, you can create an invoice to show the converted foreign currency amount.
To create an invoice in a foreign currency:
Go to Organization menu > Invoices
If previewed at this point, it will show in base currency.
Click on the ellipsis and go to 'Switch layout'.
The dialog will show all the different invoice templates.
Select the invoice you created with the foreign bookmarks.