Auto-Selecting something else in Scene-View?

We have some custom scene where our designer should have some limitations about how to edit things in the scene view. Most of the stuff is not super critical, but one thing would be really nice: If the user clicks on some "wrong" object, it should auto-select the correct one based on some internal logic. (E.g. clicking on some specific child object, which has a large mesh auto-selects the small parent-object which is the one the custom scene is meant for).

I tried the straight forward way of just re-assigning Selection.instanceIDs during OnSelectionChange - which does nothing (the old selection wins).

Next idea was to remember the correct selection and set it in OnInspectorUpdate, which works, but the editor becomes sloppy and also the inspector is closed and reopened. (And I suspect after some coffee, our fast designers will be still accidently change the wrong object. One common action is deleting stuff and you'll be amazed how fast they can click-Del-click-Del).

Another approach: Is there a way to overriding the way the objects get selected in the scene view? I know about HandleUtility.AddDefaultControl to capture the "no selection", and probably HandleUtility.AddControl might help me here, but I can't figure out how to use it correctly. (In the layout pass of OnGUI, where I use to use AddDefaultControl, I don't even know whether the user would select anything)