Stem holding shower head broke off at threads. Some threads still screwed into pipe in wall how to get it out without damaging wall?? :(

The chrome over brass shower arm's threaded into a drop eared ell,(see image) in the wall. I use two methods to retrieve broken threads. If the pipe's broken off leaving the broken threads intact in the drop eared ell I use a 1/2" Easy-Out,(see image) to grip the threads and turn them out. If the threads are split I go in with a small sharp chisel and get under the threads to peel them up and out. Good luck, Tom