I was typing a wrong response but I can tell you why it doesn't work: lasers run parallel and it's kind of an important aspect of them. In order to mix something, they need to converge. So you need to adjust the focus point of the two lasers to account for distance. I was thinking maybe fiber optics but that wouldn't change the fact you can't change the position of light in that way or it will diffuse or not converge to mix the colors.