Hi,
There is a workaround
The solution is to use the old proxy system and related actions. It's still on the Ecosystem. Then them old actions do target any gameobject, they internaly add the necessary proxy to the gameobject and your action can get infos from an fsm that sits in another GameObject that is not the IK target.
Let me know if you struggle with this. When you'll import that ecosystem package it will overwrite the official actions, so you'll need to fiddle around. I would simply only import the actions you want to use ( GetAnimatorIKGoal) and leave other actions untouched.
Bye,
Jean