1)Before Publishing the data source save the file ,
2) Publish the data source
3) Once published your ,NAS data source changed to tableau server data source
4) Close the workbook without saving
Open the saved file before publishing , it will show the data connection still connects to NAS drive.
Hope this helps.
Plz mark this answer as correct/helpful to close the thread.
Thanks for you prompt response. From what you say this is expected behaviour? It would be great if there was a setting to keep the Desktop version as it is without going via the Server.
Really helpful though, that will get me up and running anyway :-)