FetishMaps provides "Virtual Defogging" via MiniMap, matched to the main map and set to semi-transparent.
MiniMap displays all maps without fog or Icons in a dedicated window that can be made fully transparent. It also includes a button for overlaying the main map. Set MiniMap to like 50% transparency and overlay it. This gives the appearance of 50% transparent fog. Icons and pointer also appear to be 50% transparent, but at least you can see the map