Increasing Stock Through File Import?

Hello All

I regularly use a spreadsheet to do stock takes and then use import to overwrite the old stock levels.

I wondered if there is anyway to get the import to add to the stock level already on the site rather than to replacing the exisiting number in stock.

E.G. I get a delivery of 2 whatsits from a supplier, I already have 1 whatsit in stock, instead of uploading a spreadsheet with 3 whatsits on it I would like to tell CS-Cart to add 2 whatsits to the level already maintained by the site.

Anyone know if this is possible?