Choose nodes from multiple data sources in Grafana

Problem: I have multiple data sources in a dashboard and right now I’m only able to select nodes from the data source I’ve selected.

Expected outcome: I would like to use the multi-value option for the data source variable to choose more than one OpenNMS instance in a dashboard and get a list of nodes from all data sources.

Example:
The instance chooser should get mutli-value option and the nodes list should contain nodes from all selected OpenNMS instances.

OpenNMS version: 25.1.2
Grafana version: 6.6
HELM version: 5