Instead of a setpos loop, try looping the "crawl forward" animation on the soldiers. If you make sure they point the right direction, that should make em go right up the cliff.
On a side note, I was working on a rapelling script for the ECP, which basically does the opposite of what you want (makes em go DOWN cliffs/buildings/etc.). It runs on basically the same idea I just told you: a continuous, looping animation to force guys to move.