Depending on your data source, if the values are in a related table, you might be able to use a left or right join.
Depending on the other criteria of your view, you can change the level of the filter according to the filter hierarchy:
In this way, you retrieve the data from the data source, but do not display all of it in the view.
The last option is to have a data "scaffold," which is a source with all of the category values, that you blend with the data that you want to aggregate against it.
I hope that helps. If you provide a sample packaged workbook (.twbx), I could be more specific in showing examples.