Thank you K1TTT and Jim.

I am not going to swap the whole line for a self-supporting type with
steel wire in it. I have plenty of spare coax at the low end to cut
out the potentially crushed bit and just shift it up.

K1TTT: yes, you correctly point out that the goal is to avoid undue
stress, and the last several yards can be left hanging.
Iterating back, the simplest trick of all will be to
- pull it up much of the way
- tape it to the steel rope in at least 3-4 points by taping them
together for at least a couple of feet
- let the span between two tiepoints hang somewhat loose.

Thanks again!