Variance Analysis in Cube View

I have a column set that is doing essentially the same thing. Here's how I accomplished what you're asking for.

My columns:

Col_Month                             Col_MonthComp                        Col_Var           %_Var%

Select Scenario/Month 1       Select Scenario/Month 2           Variance $       Variance %

The third column (Col_Var) uses BWDiff to calculate the variance based on the account type.

Here's my member filter:  GetDataCell(BWDiff(CVC(Col_Month),CVC(Col_MonthComp))):Name(Var $)

The fourth column (%_Var%) then divides to calculate the variance percentage

Here's my member filter:  GetDataCell(Divide(CVC(Col_Var),CVC(Col_MonthComp))):Name(Var %) 

For your GetDataCell issue, you'll need to use column &/or row overrides to have the variances columns calculate properly.  I'd try to avoid using the GetDataCells in the rows, by using alternate hierarchies where possible.