Here's a partial solution--old, cheap, yet elegant, I think:
-Get yourself some aluminum (not plastic!) window screen material at a hardware store and spray paint it liberally with flat black "barbeque" paint. It's called barbecue paint because it holds up on hot surfaces.
-Use an old pair of scissors to cut the screen to size. I usually make squares, a couple of inches bigger than whichever reflector I'm using.
-Fold the corners of the screen to hold it in place over the reflector.
-If you're going to use this for portraits, give it a dry run first. The paint might smell bad the first time it gets hot. After that, no problem.
-Use two screens if you like. They'll still allow plenty of air circulation, so even if the screens themselves get warm you won't risk overheating your heads.
-If I remember right, one layer blocks about a half stop, two layers close to a full stop.
-Unpainted screen is also useful if you want to suspend bits of gel, gobo material, whatever, in the light beam.
-Remember! Aluminum conducts electricity! Stay awake!
MB