If I understand what you’re trying to do…You have drag/dropped car images into each of the viewports to make picture frames?
If you have done this, you should have a surface (“PictureFrame”) with a side view of the car on your world XZ plane. If you dragged and dropped, the texture should be applied to the “Back” View of the surface as well. i.e. if your camera is looking at the XZ plane from the positive Y direction, it’s like you’re looking at the “back” of the image.
If you have gotten the images into Rhino in a different way, you may not be able to see the image from the back. In this case, you can erase and use the preceding procedure, or simply mirror the front view surface about the XZ plane.
If I misunderstood and you’re just trying to get a “back” viewport, you can just right click on one of your viewport names, select new viewport, and then drop down the name, go to set view and select Back.