Pox made customized mapping tools for custents, which I've adapted to hmap2 (unreleased for now but see code in svn). Relatively minor changes. Seems to work so far. I couldn't find a good shot of it, but one drawback is that multiple layers of glass (transparent brushes) are not supported at the moment. A window behind a window just looks like a hole in the wall. Although, transparent entities and particles are still layered.
This first shot is confusing but it is a window looking out onto a rather ugly skybox.

