Splitting Heightmaps

I am looking for a way to slit up the rendering of a 4096x4096 height map into 4 1024 pieces. This is easy enough to do but I am using some macros such as river_run that when you move the camera they follow it around. Is there a way to design the entire terrain in one pass then zoom in on a smaller area to build it without my features moving around while trying to track with the camera movement? Or better yet is there a plug-in that will automatically split the height map into smaller chunks just to render it and then sew them back together after the rendering of the pieces? Right now I am running out of memory even though I am using full memory conservation mode.

Right now, no. The closest thing you can do is to save the file and load it again on a new world. The “splitting” of the file can be made when reading it, with the File Input device.
But as of yet, you can’t slice a terrain into chunks and merge them again for a final image.