Sort PDF Output

I have a variable product on a store site where the customer uploads their own excel file. The excel file is basic: FirstName, LastName, Address1, Address2, City, State, Zip. The variable product is set up to compose and output to a PDF file.

Our issue is that the customer is not always the best at pre-sorting their excel file based on the zip code column prior to uploading to the store site.

Is there a way to set up a callback rule using "OnJobStart" to sort the file ascending based on the zip code field, prior to composition? Just need to end up with a PDF file where the records are sorted by the zip code.

Thanks.