GetSummary breakfield question

[T.J.]

I often use the GetSummary calculation but I'm trying to figure out how to do the following.

GetSummary(summaryField;breakField)

I would like to allow to be able to "choose" from a value list of field names in the table for the breakField.

So if in my table I have 3 fields

CUST.NUM

PROD.NUM

SALES

The summaryField in the calculation will of course be SALES. I've created a field called BRKField that references a value list with the field names.

CUST.NUM

PROD.NUM

I could would like to choose one of these fields as the breakField in the GetSummary calculation.

Any help on how to do this would be appreciated.