Kryptos : K1. What is the origin of the "palimpsest" keyword? I'm studying the Kryptos sculpture with its cryptographic puzzles K1 to K4.

I understand that the keyword "palimpsest" was reverse-engineered using the tableau (and brute-force computer processing), but Sanborn always said that all sections could be solved using pencil and paper. 

There are theories about the Morse, but I haven't come across a good explanation of how to tease "palimpsest" out of it.

I've been frustrated trying to find this in the Kryptos Yahoo group.

I'm not concerned that it has any "meaning" just whether or not there is any other way to derive the keyword other than brute-force, from e.g. the Morse code.
It was never determined how to derive the keyword PALIMPSEST from the sculpture or its text. It was, as you stated, found by brute-force hill-climbing algorithms.

One theory is that crib-dragging the morse phrase SHADOW FORCES reveals IMPS at SHAD, and working form there retrieving the entire keyword, but I find this far-fetched and implausible.

The keyword for K2 can be found by crib dragging morse phrases, but for K1 it´s still a mystery.