Rotating Viewport 90 degrees?

Anyone know how to rotate the view displayed on a viewport? I'd wanted to show my camera's on a monitor mounted sideways. After finally purchasing the ViewPort it appears its not possible to rotate the view?

Any help?

Anyone know how to rotate the view displayed on a viewport? I'd wanted to show my camera's on a monitor mounted sideways. After finally purchasing the ViewPort it appears its not possible to rotate the view?

Any help?