Help with secondary axis on Waterfall Graph with 2 scenarios

Good evening,

I am having trouble creating a secondary axis on the attached sample Waterfall chart to show the Gross Margin Variance - B/(W) range of data. I created the Waterfall Chart with minimal effort but my challenge seem to be with representing the GM Variance on a secondary axis (preferably the same column chart type) and also to be able to make the data ranges on the Y axis on the secondary axis should be such that the column/bar charts are the same size as that of the Revenue Variance bar charts created.

I hope my request makes sense. Simply put; from the attached I am trying to create a secondary axis so that my bar charts in the Gross Margin section are the same size as those in the Revenue Variance section on the same graph if this is possible.

I would really appreciate your direction and help.

Best Regards.