Hi Mike,
As said by expert Ramagiri, in standard SAP transaction CS12 you cannot see stock and you need to develop report.
But if you do not want to develop report then another way to work out is to copy all the exploded BOM items and pass them to MB52 transaction (Display Warehouse Stocks of Material). From MB52 you will get the stock of exploded BOM items which you can copy and paste to you excel sheet column for respective items.
Regards,
Narresh