Implementing Real Analysis Services DrillDown in a Reporting Services Report

Sean Boon recently blogged about an approach to implement drilldown on charts with Reporting Services when Analysis Services is used as the data source, and it got me thinking about ways to implement drilldown in Reporting Services in general. There are two standard methods used to do this that are widely known about:

• The first can be described as "fetch all the data you're ever going to need to display and then hide the stuff that hasn't been drilled down on yet" - this article describes it well, albeit for SQL data sources. It's easy to implement but has has big problem: if the amount of data your report could ever possibly display is massive then the report will be very slow to run, for example if your dataset query returns millions of rows.
• The second is more scalable, in that you have multiple reports for each level of granularity you want to display and when you drill down or drill up you click on a member in the Report and pass it as a parameter to another report. This also works well but has a different problem: you now have multiple copies of what is essentially the same report to maintain and keep in synch. This approach can also only display one level of granularity at a time, and sometimes it's nice to be able to see multiple granularities in the same report.