While it looked promising, I also found a lot of people who were making DIY versions of this. I decided to try making one myself.
After digging around my closet for a couple of minutes I found the materials needed to do it. All I needed were two things:
a 3-point military sling from my airsoft MP5 submachine gun
Bogen 3157N Quick Release Plate
Assembly was simple:
attach the quick release plate to the bottom of my camera
connect the D-ring on the bottom of the plate to the sliding clip on the sling. That's pretty much it.
I've used this on a recent wedding shoot and it seems to perform pretty well.
There are a few minor issues with this DIY version - there's no adjustable brake, it's a little difficult to adjust the size of the loop, the clip does not lock like the Black Rapid mini carabiner, and I'm not sure how strong the D-ring on the Bogen plate actually is. I'm pretty sure Bogen never intended for their camera plate to be used in this manner:
While my DIY strap not as fancy as this Black Rapid is, it does do about 90% of what the actual product does. I figure it will hold me over until I can check out the actual Black Rapid product in person the next time I hit the camera stores in Tokyo.