Can you import the client's data into a database, SQL or access it similar do your ETL work either during or after import then connect to the tables directly during your data load taking the Excel/csv conversion out of the equation all together?
Suppose I could establish an SQL DB, but that would add another layer of complexity in my process.
All of my ETL work is performed prior to loading into Sense, and so far I haven't seen if Sense has the same capability my ETL tool currently has (my largest data cube to date is over 65M lines from 123 different systems).
I ended up replicating my app, clearing the data in the Data loader editor, and re-establishing the links with the appropriate file types etc.
Seems to have worked okay, was hoping for a "on the fly" source switch..