Any Control Rig Experts that can Help me solve this issue.

I am working in VR and using control rig to handle all my IK Body logic, but there is something I have been planning to solve and I wanted to ask the community and specifically any control rig Experts the best way to approach this .
Basically I want to control the positions of the characters elbows from the wrist transforms As demonstrated here! in this video clip VR wrist control of elbow positions

This was the short description of how they did this when I asked But its not enough for me to go on. and The solution is UE4 specific.

The solution does not have to be the exact method they used, Just yield the same results.
I thought about using Joint rotation constraints But I would like some feedback on methods before I do the work Thanks