This morning, I've finally got something to show for it. I went out an purchased the Alumilite starter kit, which came with enough mold rubber and resin to get me started. At 40 dollars, it wasn't cheap. However, since I've never had the opportunity to make a two-piece mold, this was the perfect excuse to learn. The process works very well, and the resin sets in an astonishing 3 minutes.
While the first copy isn't absolutely perfect, it should be good enough. The main rocker hinge is made of stainless steel in my copy, so it won't wear out too quickly. This is the same rod I'm retrofitting all of the remaining original switches with, as all of the little nibs are in poor condition or broken off completely.
All in all, the process was a success. I can crank these out fairly quickly now. If there is interest from other PDP-8 owners to get some replacement switches, I might even be interested in producing some for sale.