Ashley Schroder has written a Google Docs/Drive adapter for the ImportExport module. It's not dataflow and it's fast!
If you really want to do additional processing before doing an import, you may consider using an array-based ImportExport extension such as ApiImport. An added benefit is that it takes care of a bunch of stuff for you (such as indexing). In that case you would have to write the glue between fetching google docs CVS, converting it to an appropriate format, and doing the import.