I'm kicking myself for not having thought to do this years ago (like 2014/2015). It's fundamentally so simple a job it's stupid. Adding two square sheets perpendicular to each other, and providing opposite surfaces, for just four sides and eight polygons.
Actually, why *no one* twigged onto it is kind of astonishing. Untold hours have been expended by so many to make up whole new objects (some fictional!), while an easy fix to an existing deficiency in a rather important element had to await stumbling onto for so many years.
And it's not like this is some radical concept. Already there are tree/bush objects built using this very technique!
To mount my soapbox again, for a moment. I really wish there was more effort given to improving existing deficiencies. For example. Many objects lack shadows. Others at the longest range LOD have roofs placed at ground level and hence flicker. (Similarly, many damaged structures with exposed floors flicker at long view distance.)
A project could identify what needs redress, and the work apportioned among a group of willing modders. Many hands make light work, as they say. I'd be game.
Alright, I'm back down from my soapbox.