There's a community plugin to work directly with Google Sheets, reading and writing information:
https://github.com/jfmonteil/Pentaho-Google-Sheet-Plugin
If you are able to work with Google Spreadsheets instead of generic csv files or Microsoft Excel files, it might work for you instead of looking for a workaround managing the Google Drive part with another scripting tool and then calling the script in a PDI step.
Regards