Maybe it is as simple as a furniture item called "wall section" that is therefore sizeable and has the inherent ability to add at a prescribed elevation?

That is where you should use an extra level. I know, it's not on the same level but it does exactly what you you want: it's elevated and acts and displays as a wall. The solution Daniels118 offered certainly works but as he said, you will have to create a custom object for it and optionally a 2D icon. But that also means an extra object that shouldn't be there. That is a perfect solution if the hole you want is custom, like a triangle under a staircase (see this how-to ).
To create such an object you use a box, triangle, or other object to act as the hole. Export it to an obj/mtl file. Edit the mtl file and set the transparency for the materials by adding "d 0.0" at the bottom of each material section. Save and import the object as a "Door or window" and you can create you opening.
The only other alternative is to use an elevated box as the stub wall but be aware that unfortunately a wall and box both textured with the same texture will not look the same.