Ok, one method is to append data rows with labels but empty data to your datasource and before the Pivot process. For example, you could use the AppendRow process like this:

$this->src("myDataSource")
...
->pipe(new \koolreport\processes\AppendRow(array(
    array( "type" => "Hispanic or Latino", "subtype" => "Central American", "vaccine" => "Astra Zeneca", "doses" => 0), // we add empty/null/zero measure data so that data aggregate is not affected
    array( "type" => "East Asian", "subtype" => "Vietnam", "vaccine" => "Pfizer", "doses" => 0), 
    ...
)))
->pipe(new \koolreport\processes\Pivot(...))
...

Let us know if we understand your problem correctly. Tks,