Use a chain saw!!!

That's what my parents do with their HUGE zebra grass clump. It was planted (transplanted actually) in the early 80's and was part of the original farm that is centuries old. Every spring my father tries to thin it down a bit by offering everybody clumps from the side of it, but it just keeps getting bigger and bigger. They no longer try to cut it back in the spring, he just whips out the trusty chain saw and with a few well placed swipes the trimming is done!

By the way, I tried not cutting back one of my clumps (too lazy I guess) a few years ago and I wasn't happy with it. Now I see it more as a start of spring:

Winter sow annuals
Plant tomato / pepper seeds
Cut back zebra grasses
Prune the roses...

Ah! Spring is right around the corner!

When it comes to trimming back those huge clumps of dead grass, I think a lot of avoidance is due to the MESS. Neighbor ties twine around her pampas; divides it into 4 or 5 sheaves, each with three or four rows of twine pulled as tight as possible. Then she cuts across the bottom of each shock, which gives her an already-tied bundle that can be carried away. I always think of those old engravings of wheat shocks when I see those bundles.