Hey Chris -
There aren't tons of people working with the TDM in Tableau yet, so I'm guessing you won't get a huge response to this question. We also don't yet officially support connectivity to the TDM, even though it works pretty well.
That being said, let's give it a shot. If worse comes to worse, you'll be able to write MDX to take care of this.
Is there any way you can show me what you want using the AdventureWorks TDM sample? That way we can look at the same thing vs. trying to guess at it. Maybe point at the AW tabular model and then post the workbook?