Wow, I actually never thought of that! I'm just wondering how to prevent the molds from gluing shut. Would the plate prevent the two halves of the mold from touching?
You would need a plate for each side of the mold. In effect, the plate forms the entire touching faces of the mold, and leaves a cavity in each side. When the two poured silicone halves are combined, the mold cavity is formed.
The plate could also be in the form of a cup, ready to pour in silicone and make a mold.
In theory this will work great, but keep in mind that items like keyed bumps need to be designed into the mold plates so that the mold halves go together properly.
See pictures below for an example of mold plates for a simple extended 3x3x3 edge.