I think this hack is fun because there are lots of ways to pull it off, I suspect. I started work on one too, here are some pics.
CAM00083.jpg
My casting setup, with megablocks, clay, and a magnet. This cast failed, it needed to be larger. Setup is the same though.

CAM00086.jpg
Successful casts with flash still on.

CAM00087.jpg
Trimmed, and you can see the magnet through the plastic a little. I will be coating it in silicone sealant, so it's cool.

I'll get some pics of the housing when its done, hopefully tomorrow.