Okay, here's a script that sets the FABRIK 3D magnet position based on the position of a Position3D node. Just apply this script to a Position3D, setup the inspector variables, and reload the scene, then it should work :)
Google Drive link: https://drive.google.com/file/d/1DnFXr8oK8ZUgtn-c4M0kMqHjcP-FGf5M/view?usp=shari...
I'll include the script in a folder called "Utility_Scripts" in the next release of Twisted IK 2 with the development example project as well, so anyone in the future can also benefit from the script.