Topology Reports - template view with drop down list parameter values

I'm trying to create a Topology Report from a Template View that has a drop down list for the user to select a parameter value from; however I'm only able to create an input box for the user to type the parameter value in.  Ideally, the drop down list would be populated from a query.

 

The Custom Reports have the drop down lists in them, the Application Breakdown Report for example has a list of countries to select from, which then populates the states and cities drop down boxes accordingly, but I can’t find these reports to see how they did it.

 

As a workaround I’ve created a web page where you can select the parameters first and then view the report from a generated link. 

 

Thanks,

Bill