Sorry, here's the photo: https://i.imgur.com/fx8mGat.jpg

Turns out it was a bit of rot so I cut it back to this: https://i.imgur.com/GV0P4WX.jpg. I also removed the flowers totes and focus its energy on making stems. It already seems pretty dry so maybe just a few days until it calluses over.

So, how can I get this plumie to root? Stick it in well-draining soil after it calluses and limit watering?

How is your cutting doing? It looks like your post was missed, maybe people thought you had gotten an answer, sorry you didn't get an answer!

If I'm not too late, what I can see from your picture is that it appears the center is still trying to pull back on the cut you made - has it calloused over? I used to have a really hard time getting a good callous until someone posted about wrapping the end in Cling Wrap and taping it with scotch tape & letting it callous that way. I like to lay the end on a heat mat too and that has really increased my successful callouses.

Once you have a successful callous I would pot it up in one of your cups with drainage holes drilled in there or a Gatorade bottle or something similar with holes drilled in the bottom and put it in a very well draining mix of potting soil and perlite. Then sitting it on a warm surface like a heat mat or warm concrete (without direct sun exposure) will help a lot. They like bottom heat to stimulate rooting. I hope this helps and hope your cutting made it!