Flatten area with BGLComp

I seem to recall this can be done, but can't find it anywhere.
Building exclude areas is no problem, but I have read and reread the tutorial that came with the Compiling Scenery with BGLComp SDK, and I just don't see any referance to it.
So does anyone know if it is possible to create a flatten area using BGLComp?
Building exclude areas is no problem, but I have read and reread the tutorial that came with the Compiling Scenery with BGLComp SDK, and I just don't see any referance to it.
So does anyone know if it is possible to create a flatten area using BGLComp?