I cannot say how to do this using the new waterfall specialty chart. It seems that the new specialty charts are rather limited in options, so it may not be possible to have a "stacked" column for one of the main endpoint columns.

The "old fashioned" ways of building waterfall charts should have no trouble incorporating a stacked column for the first column. If you are not familiar with these methods, here's a good tutorial: https://peltiertech.com/excel-waterf...bridge-charts/