I don't know squat about SSAS. Can it actually use a T-SQL query where you need it? If it can, I have a high performance method for doing this. It may require dynamic SQL based on your request but that should be no biggee to do in an SQL Injection Proof manner. It will require some new indexes if they're not in place already.
--Jeff Moden
Change is inevitable... Change for the better is not.