How to enter backdated stock moves?

As far as I can see there seems to be no way to enter backdated stock moves using standard OpenERP functions. For example, in Physical Inventory function, you could input a past date in 'Date Done' field in the header but once you press 'Validate Inventory' the field gets updated with the current date, which is not great when you are trying to set up initial inventory in an implementation. I would like to know: - if my above understanding is valid, - if there is some workaround, - what the rationale is of the current design