Which version of the Excel importer do you have? The latest version should do exactly what you are asking for.
Typically as a rule I stay away from direct imports and rather to import to an "Import Entity" first so I can do further data manipulation from there. My import entity typically mimics exactly what the final entity will look like but with additional attributes like "Import Status" and "Warning Message" in case you ever have bad data you are trying to feed the system.
Just to be clear, the updated version incorporates a new replication.jar file, there is a chance that you've updated your importer but that file did not update.