Distinct user hits for all levels of a calendar dimension.

I am attemping to count distinct users for web page hits in a SQL Server 2008R2 SSAS Cube. My fact data comes in at the activity date and web page level with character user id. My distinct count is only good at that level. At the monthly quarterly and yealy it adds it up as expected. Is there MDX I can use to calculate the distinct users at all levels of my calendar dimesion?

Thanks

Steve