As per my understanding, there is no such easy way to do, like with XP or FSX. The only way appear to me to use the 3D Tools like 3DMax or AC3D
Another possible solution could be to create an geotiff with QGIS or ArcGIS from a 3D elevation data source where each Grey scale value is assigned to a certain height. Theoretically it should be possible to manually edit this tiff file with Photoshop or GIMP or whatever and then draw a polygon around an area with exactly the grayscale value that equals to the height you'd like to set, but I guess this would mean an awful lot of guesswork and trial and error.