Can I Set the Business Date in Import Scenario

I have reports and dashboards that rely upon an Opportunity Stage being set to Won (along with the Opportunity Status) when the Opportunity is Won.  I have hundreds of opportunities that did not end up this way.  To change the Stage, I have to reopen the Opportunity, change the Stage, and Close as Won.  Easy enough to do with an Import Scenario, but I really need to preserve the original Closing Date.  Seems resetting the Business Date for each line of the import would do this for me if possible.  Very open to alternatives (we are hosted).