FABRIK - switch fron Bone Space to World Space realtime

Hi, I’m just starting to learn IK. I need to make character’s hand reach the target in the world coordinates.
The problem is that when compiling, if End Effector is in World Space, and the target is not yet assigned, the hand turns out somewhere toward the center of the body. And everything looks normally only in Bone Space.
So I need to switch between the Bone space and the World space inside the FABRIK node. I want to find rialtime access to it.
How to do this?
Maybe in C++? What class should be inherited from? And how to get this parameter?