Cube Generation Algorithm

I have a randomly generated array of cubes, each one has its position and color. That cubes are placed on a field, the field size is 5x5. Each cube is connected with at least one another cube. I need to add a "floating cube feature". That means that I need to randomly add a cube that doesn't have anything below/above it but is connected with another cube by one side ( see the image) What I need to add: Array of cubes on the image:

var cube_arr = [{posX: -2, posY: 0, posZ: 1, color: "red", row: 1},
{posX: -2, posY: 1, posZ: 1, color: "red", row: 1},
{posX: -2, posY: 2, posZ: 1, color: "green", row: 1},
{posX: -2, posY: 3, posZ: 1, color: "purple", row: 1},
{posX: -2, posY: 0, posZ: 0, color: "blue", row: 1},
{posX: -2, posY: 1, posZ: 0, color: "blue", row: 1},
{posX: -2, posY: 2, posZ: 0, color: "blue", row: 1},
{posX: -2, posY: 3, posZ: 0, color: "green", row: 1},
{posX: -2, posY: 0, posZ: -1, color: "red", row: 1},
{posX: -2, posY: 1, posZ: -1, color: "red", row: 1},
{posX: -2, posY: 2, posZ: -1, color: "red", row: 1},
{posX: -2, posY: 3, posZ: -1, color: "purple", row: 1},
{posX: -1, posY: 0, posZ: 2, color: "green", row: 2},
{posX: -1, posY: 1, posZ: 2, color: "purple", row: 2},
{posX: -1, posY: 0, posZ: 1, color: "black", row: 2},
{posX: -1, posY: 1, posZ: 1, color: "red", row: 2},
{posX: -1, posY: 0, posZ: 0, color: "black", row: 2},
{posX: -1, posY: 1, posZ: 0, color: "black", row: 2},
{posX: -1, posY: 2, posZ: 0, color: "green", row: 2},
{posX: -1, posY: 0, posZ: -1, color: "blue", row: 2},
{posX: -1, posY: 1, posZ: -1, color: "blue", row: 2},
{posX: -1, posY: 2, posZ: -1, color: "green", row: 2},
{posX: 0, posY: 0, posZ: 1, color: "red", row: 3},
{posX: 0, posY: 0, posZ: 0, color: "black", row: 3},
{posX: 0, posY: 1, posZ: 0, color: "red", row: 3},
{posX: 0, posY: 0, posZ: -1, color: "blue", row: 3},
{posX: 0, posY: 1, posZ: -1, color: "red", row: 3},
{posX: 1, posY: 0, posZ: 1, color: "red", row: 4},
{posX: 1, posY: 1, posZ: 1, color: "purple", row: 4},
{posX: 1, posY: 0, posZ: 0, color: "black", row: 4},
{posX: 1, posY: 1, posZ: 0, color: "blue", row: 4},
{posX: 1, posY: 0, posZ: -1, color: "red", row: 4},
{posX: 1, posY: 1, posZ: -1, color: "red", row: 4},
{posX: 1, posY: 2, posZ: -1, color: "purple", row: 4},
{posX: 1, posY: 3, posZ: -1, color: "yellow", row: 4},
{posX: 2, posY: 0, posZ: 0, color: "green", row: 5},
{posX: 2, posY: 1, posZ: 0, color: "green", row: 5},
{posX: 2, posY: 2, posZ: 0, color: "yellow", row: 5}]