Place one label per part on web map or map service (duplicate labels)

[FionaRenton1]

I want to place one label per part on a multi-part polygon feature class on an ArcGISJavaScriptAPI web map.

Sometimes the multi part features are not adjacent to each other like in this map using ArcPro.

In ArcGIS Pro this is done by using the menu: Label Placement duplicate labels: one label per part.

I have tried publishing a web map with the labels on, but the webMap does not read the duplicate labels and so only one label is displayed for GH.

I've added labels using the JSAP, but I cannot find an option for placing duplicate labels.

I think it should be somewhere in the labelClass placement properties, but I can't see it. 

Is my only option to create a single part featureClass for labeling?

Thanks!