I shouldn’t be up now, so I’m not going to implement something for you.
The idea is that you could have a single DIV holding a chart.js graph that is positioned (and sized?) to be just like the Picture showing a chart in a Node. The click event handler could position that DIV, which has a z-order such that it is in front of the diagram’s DIV, so that it exactly overlaps the Picture in the Node. And you set that chart.js graph to show the same data that is shown in the node.
When the user clicks elsewhere, you hide that DIV with the chart.js chart.