Add an "OnContextClick" message to any open Unity Editors.

SceneContext.cs

using UnityEngine;
using System.Collections;
using UnityEditor;
using System.Reflection;

[InitializeOnLoad]
public static class SceneContext
{
    static System.Diagnostics.Stopwatch clickClock;

    static SceneContext()
    {
        clickClock = new System.Diagnostics.Stopwatch();
        SceneView.onSceneGUIDelegate -= OnSceneGUI;
        SceneView.onSceneGUIDelegate += OnSceneGUI;
    }

    static void OnSceneGUI(SceneView sceneview)
    {
        if (Event.current.button == 1)
        {
            if (Event.current.type == EventType.MouseDown)
                clickClock.Start();
            if (Event.current.type == EventType.MouseUp)
            {
                clickClock.Stop();
                var period = clickClock.ElapsedMilliseconds;
                clickClock.Reset();
                if (period < 300)
                {
                    EditorApplication.delayCall += OnContextClick;
                    Event.current.Use();
                }
            }
        }
    }

    static void OnContextClick()
    {
        foreach (var i in Resources.FindObjectsOfTypeAll<Editor>())
        {
            var mi = i.GetType().GetMethod("OnContextClick", BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);
            if (mi != null)
                mi.Invoke(i, null);
        }
    }
}