Just seen this over on Stan Winston's facebook. God, I wish this was the design in the remake. Badass!! https://www.facebook.com/StanWinstonSchool?hc_location=stream
use the landscape actor http://udn.epicgames.com/Three/Landscape.html you can set individual pieces of a single landscape to stream in and out separately
Make a new shortcut and add -NOTEXTURESTREAMING after the .exe to turn off texture streaming. More info: http://udn.epicgames.com/Three/CapturingCinematicsAndGameplay.html