For this kind of logic to work within InDesign, you need a script. Data Merge is pretty simple -- no different from the "Mail Merge" you find in word processors.
Without a custom script, you have two choices: create the correct number of individual lines in the original CSV or create one instance of each label and print it the appropriate number of times by entering the appropriate number in the "Copies" field of Acrobat. Printing multiple copies of each label from PDFs is considerably faster than printing multiple instances of a label from InDesign, because of the different amounts of processing involved, so even with a custom script you may not be happy with the speed of your output.
Which approach would work best depends on how you're generating the CSV in the first place, so I can't really give you any guidance in that regard.
I'm assuming that this is not a one-off situation, but something that you will have to build into a standard workflow for the future. If so, it's worth investing some time into developing and testing different approaches to see which will work best.
Faced with the same situation, I would probably look first to my database or order-processing application to see whether it could generate a fully populated CSV to drive Data Merge. If that wasn't feasible, I would probably head over to the Adobe InDesign and Acrobat scripting forums and ask for help. Scripters are an amazingly helpful bunch of people, and it's quite likely someone will reply with the exact script you need.
