Well, after trying to make a five mile map and find that there is no way to set the rasterizer's far clipping distance - by scripts or commands - I had to resort to memory hacking. Thanks to Patrickssj6 and the Tsearch program, I was able to find the correct addresses for the far and near clipping distances in Halo and I wrote this program.
Instructions
Just start the program, start Halo, and when ingame press "M"
Best Used On
Any map larger than 1024 units, ie, Hugeass.
Warning: Does not work on Coldsnap because of all the fog. Turning off fog will allow you to see further, however.
Pics

Before Far Clip Fixing:

After Far Clip Fixing:

Edit: Link fixed... We had to move the site to a new host, so the file got moved.