Well, how can you rotoscope the snow cone part from the 3D Blu-ray onto the 2D footage if it’s in 3D?
People on YouTube have been able to separate the left and right eye views of 3D Blu-rays, so you could pick which eye view best matches the shot. The left eye view might be the best bet, but I could be wrong. I think you can use MakeMKV to do it.