Just a little while ago ASLoadSim was realeased on CodePlex. It "...contains a set of utilities used to generate a query load and test the scalability of Analysis Services server...". Sounds great to me!

 Included as part of the distro is an whitepaper around SSAS load testing best practices.

 Here's the link!

http://www.codeplex.com/SQLSrvAnalysisSrvcs