The ideal way to do this would be to bring over a high level character from a previous save and go and beat him on normal or TVH mode, solo. But, not everyone has a previous save...so, you can party up with 3 other people or attempt to use the glitch spot shown in the video below. It isn't 100% effective from what I've found.
The video below shows the "glitch" spot that doesn't allow you to get damaged by Terramorphous.
Some additional helpful information...when you get downed while fighting Terramorphous, you respawn down by the vending machines and have to run all the way around the curve and up the hill.
There is a shortcut. When you cross the first low bridge, turn right and drop off the edge. You'll drop onto a metal platform that carries you to the top of the hill.
This will save you around 30 seconds each death. It's not huge, but after dying several times it gets very annoying having to run the long way.