Webi report - Excel Source - breaks if excel is edited

I have a Webi Report that uses Excel has its data source. I have many variables defined in the webi report. Now, I had to add a new column in the source excel. When I do that, all the variables in the webi report break. Is there a way around this? I want to add columns to excel and not break my variables. Using BO 4.0 SP5.