Have you figured out the solution to your problem?
Based on my understanding, you want to get the local space of a particular bone but set it in global space?
Have you tried tinkering with calling the node GetSocketLocation(FName) which returns the location of a bone in global space. You can do this in the update event of your AnimBP and pass it into the ControlRig. Then you can pass that value as the effector of your IK function in the ControlRig.
If you want more control you can also create a control/virtual bone and set the virtual bone in Global space and use the “Get Transform - Bone” node to get the bone in Local space if you want the local value of the bone.