How to Customize the Dropdown List in a SSRS Report that Uses a SSAS Cube Data Source

I have a requirement to develop a report that uses a SQL Server Analysis Services Cube as a data source. The report must allow the user to select the desired month from a dropdown list. The dropdown list must include the last 24 months of available data with the default value being the current month. The administrator must have the ability to specify the current month and change it as necessary. I can create the report, but I'm having some difficulty with implementing the report month parameter. Can you give me some ideas on how to do this?