Expanding the Ultra Key with solid block

Having an issue trying to key out an area of green screen that was not shot in the original footage. So I have two areas on either side of the green screen that did not have full coverage. I need to expand my ultra key to include these areas without having to use the dropper tool to select the color I want to key. One idea was to fill the area with a solid color then select that to be keyed out in the green screen selection. Any input about this would be so helpful. Thanks.