SSAS - Using the SUM Function within a Measure Group to display a Distinct Count with SSAS (SQL Server Analysis Services)

Whilst completing my review on the Expert Cube Development with SSAS Multidimensional Models, I came across the Distinct Count Measure within SSAS and how this can affect query performance as well as processing performance. You can find the reference on page 114. And here is a link to the actual book that I am reviewing: http://www.packtpub.com/expert-cube-development-with-ssas-multidimensional-models/book

What I wanted to do is instead of using the Distinct Count Function which we can use within SQL Server Analysis Services (SSAS), (which as we know has some performance issues along with creating its own measure group), I wanted to find a way where I could use the SUM Function in our Measure group but still return the distinct count.