Extrusion of polygons with per position height

I have a GeoJSON file of polygons where most of them are sloped, i.e. their corner points have different Z values. I can import and display them nicely in Cesium with perPositionHeight enabled. What I’d like to do is apply a standard extrusion to the polygons, e.g. 10 meters, with the extrusion also being based on this per position height. So the end result would be 10 meter thick sloped polygons, looking something like this: https://imgur.com/xq3twFI

Can this be done? If not, does anyone have an idea for a workaround - maybe GeoJSON is not the best way to go here?

What happens right now when you add this extrusion? There’s code example here that extrudes polygons loaded from GeoJSON: https://sandcastle.cesium.com/index.html?src=GeoJSON%20and%20TopoJSON.html

Now when I add e.g. a 10m extrusion, every part of my polygon caps out at 10m above the ground. So the bottom of the polygon is sloped upwards as it should be, given it has perPositionHeight, but the top is flat at 10m. What I want is for it to hold its shape and in essence simply become thicker.

I’ve worked around this by creating multiple polygons representing the bottom, sides and top of the polygon, but it’d be great to know if there was a simpler way to do this.

Can you share a Sandcastle of this so others can see how this is done? See: How to share custom Sandcastle examples.

I think this may not be supported, but perhaps this can be a built-in feature if it’s a common enough use case.