On mine I just cut down the existing outer, if you cut off the zip ties you can push and pull the outer through the frame.
So I disconnected the cable from the remote (which I have replaced with a One up remote), fed the cable though, installed a new inner gear cable and the post, then fed the outer back though until the post was in the right position for me, backed it out a couple of cm, then cut down the outer at the dropper remote end. Re zip tied the outer to the mounts by the shock, but not as tight as before so some movement allowed.
This does mean if I want to fully remove the post, I have to unclamp the dropper remote and feed the outer back through the frame whilst pulling the post to get it fully out, but easy enough to do.