TacomHQ makes a lens that is positioned in front of an optic to shift the image and give the shooter a new Zero. They have lenses that can attach to a scope or a flip up lens for red dot sights. I wonder if this would be legal in Tac Limited 3Gun? The rules state you are only allowed irons or a non magnified optic. If the TacomHQ lens does not magnify the red dot image then perhaps it could be used.
Here is a video they posted shooting an AR out to 500 and 1000 yards.
Their website is a bit sparse. No mention of price or availability.