What you could do is to set up a manufacturing process (of type manufacture, not kit) converting a lot number tracked purchase item to a serial number tracked sale item. Your traceability report would look like this then:

However, I would rather advice you to give it a good thought why lots come in and serials go out. Is transferring to your stock while purchasing with serial number that much more effort or, for what ever reason, impossible?
Got a barcode on your goods? The barcode app could easily distinguish lot/serial parts while scanning.