Hiding Columns Yet Use it in Data Link as Parameters

Hello:

Transformations is a great feature. It allows a field in the report to be hidden among host of other features.

However, I want to hide a column in display yet use it as a datalink parameter to a different report/chart.

This is not working. Only when I SHOW the column in the report, the datalink variable feature seems to be working.

Am I missing something? Can someone shed some insights?

-gv