I may be missing something, but it looks like you might be overcomplicating your problem.
1. Create a new worksheet.
2. Drag [Department Alias] to the Filters shelf.
3. Select 1 of the departments to show
4. Drag [Account Alias2] to the Rows Shelf
5. Drag [Measure Names] to the Rows Shelf to the right of [Account Alias2]
6. Add [Measure Values] to the Text Shelf
7. Right-click on [Department Alias] on the filters shelf and select Show Filter
you should now be able to select between departments and show only the proper associated values.
If this approach doesn't work the best way to get an accurate answer would be to post a sample workbook along with expected values. It significantly helps us in the community to be able to try out an example.