Duplicate Parameter Values in Report (SSAS as a Source)

I am creating a report using an SSAS Cube as the source. Within the report I'm displaying the following values:

Month
Year
District
City
Street
Total Requests

As part of this report, I'd like to provide a drop down parameter for users to select the "District" value. However, when I create the @District parameter, in the preview pane it shows duplicate values (i.e. valid values for District are 1-9, with multiple cities assigned to each district. My drop down displays the value "1" several times, one per each city, and so on and so forth).

What I'd like to do is only display the distinct values of District in my parameter drop down. I've read through previous forum posts where it suggests creating a separate query to select the distinct values from the table, however the syntax for those posts appears to be specific to database connections but not SSAS. (i.e. syntax given was Select DISTINCT column FROM table). This syntax doesn't appear to work with SSAS Cubes.

Could someone please offer some assistance on how I can extract the distinct values for District? Thank you in advance.