ssrs 2008 r2 export to csv file problem

In an SSRS 2008 R2 report, the users are going to export the data to: csv (comma delimited) and  excel.

I am using the following to display if a column is visible or not:
=IIF(Mid(Globals!RenderFormat.Name,1,5)="EXCEL" AND First(Len(Fields!CustomerNumber.Value)) > 0,False,true).

I have set the DataElementOutput=Output for the textbox that displays the value. I have left  DataElementOutput=Auto for the textbox that contains the column header.

When exporting to csv (comma delimited) or excel, I basically want the column to be visible when there is data in the field and the column not to be visible when there is no data.

The code works for excel but the code does not work for comma delimited.

Thus can you tell me what I can do so the column is not disaplyed when the data is exported to csv (comma delimited)?