Best practice for translating budgets and forecasts with different rates?

Our company has a business need to translate forecasts within local SOB with a static rate throughout the quarter (i.e. rate defined at beginning of quarter and then not changed), while the budgets can and should be translated with updated rates throughout the quarter. Standard translation only has the option to translate budget vs. actuals, but not budget vs. forecast. We are looking for the best way to translate forecasts with a different rate than budgets. Any suggestions would be greatly appreciated!