How to make FABRIK affect only one axis?

Hey guys, I’ve based my blueprint loosely on what’s been said in this thread however my case is a bit different:

In my case I’m adjusting punch target location in real time. Everything works fine but I’d like FABRIK to only affect Height (Z axis).

Maybe it’s basic stuff but i have no idea what to put into the broken vector data as the target location is in world space / not relative to the bone.
Is there a way to make it relative?

Thanks for you time