When I started out, before I got my dual injector, I just used a piece of aluminum foil sandwiched between the mold halves and got 2 halves, then just put one side in the mold and shot the second color, worked great. Then i got the dual and wouldn’t go back, yeah you “waste” some plastic but usually I mix the sprues and come up with another good color (morning dawn makes a really nice purple for example)