Im not sure that will work... or I might not be understanding what you are doing...ha probably both. .... but here's my though of why i'm not sure it will work except on open hand pour molds. On injection molds that mold will be full upon the injection of the first color. The lam plate feeds the second color at the same time into the mold.
You could pull off a core shot with 2 injectors, or you could pour bottom side of mold, close, then inject top color.