May I register a union data source as a single datasource in druid?

Hi guys,

Has someone ever used Superset to explore druid datasource ? In Superset we can only slice over one single data source, but currently we have one query using union data source to compute some metrics, so is there any way to register a union data source as a single datasource in druid so that I can do slice in Superset on that? or some other way from Superset? thanks very much !