I would simply integrate them into my pictures using Photoshop. Add as a layer or paint photorealistically...
I have considered that. However there was a small program that could place boxes in various flight simulators but it seems to have been overcome by updates. I would prefer a parametric method like that but I will do what I have to do. In any case, with AutoOrtho I have been able to find a few airports where permanent box marking are sufficiently visible that I now have a few places to practice. If I need more boxes (i.e. for a specific contest preparation) I will probably attempt the raster method you propose.