I use Access for that.
Import the manufacturer csv into a table, create a query that pulls the data from it translated to the proper Magento column headings and then default fill the other required columns with proper name and value. Export as UTF-8 csv file and you’re ready for import.
Ever after, import CSV, call up query and export. As long as no column titles change, you’re home free from now on.
Otherwise you have to use Excel or some spreadsheet and you’re always fiddling around with creating the extra columns and doing spill and fills for the default data, a waste of time in my books.
If you want the import routine to do it directly without preprocessing, then Scott at commerceextensions.com has created many different custom import/export extensions and might be the go-to person for making this happen.
The nice thing about Access is that it’s “extensible” in that you can easily support multiple vendors without having to do code rewrites.