There is no such option as far as I'm aware, though the engine will happily render everything in front of you if level's visibility data dictate so. These optimizations are disabled in the Engine.exe which is used for 3D view rendering when you're working with the Level Editor, everything in front until the fog-point is rendered.
The algorithm for calculating visibility data at the stage of level creation is not too accurate so it can take a lot of boring clicking to properly optimize the level, depending mostly on how the terrain is shaped. Some are easier than the others.
"When a human being takes his life in depression, this is a natural death of spiritual causes. The modern barbarity of 'saving' the suicidal is based on a hair-raising misapprehension of the nature of existence." - Peter Wessel Zapffe