I've used Stadtreiter's clamp for a while but the cable and the headset are slightly too loose inside it. I made a quick version where both are slightly tightened. It works well, neither the clamp nor the cable move at all.
I included the (ugly) FreeCAD file.
index_front_cable_clamp-v2-Body.stl | 40.7KB | |
index_front_cable_clamp-v2.FCStd | 30.8KB |