Looking at the documentation and an example, the customization seems rather simple:
- To the set entity, add a yAxisID attribute, which is filled in the microflow that generates your chart;
- To the LineChart's XML, add a property through which this attribute is selected;
- To the LineChart's JS, make sure the attribute's value is read (set.dataset.get), add an JS object attribute where the _set object is created (around lines 81-91) and fill the JS attribute value with the Mx attribute value.
Good exercise to learn some widget customization!