Run script in Edit mode when paused?

What I ended up doing was writing a custom editor that operates on GameObject objects. In the OnSceneGUI() method, I put my code that I want run (which in my particular case, sets camera matrices in a shader). This works fairly well except that you MUST have an object selected in the hierarchy in order for the script to run.

using UnityEngine;
using UnityEditor;

[CustomEditor(typeof(GameObject))]
public class UpdateCameraMatrices : Editor 
{
    void OnSceneGUI () 
    {
        Camera camera = Camera.current;
        Shader.SetGlobalMatrix("viewMatrix", camera.worldToCameraMatrix);
        Shader.SetGlobalMatrix("projMatrix", camera.projectionMatrix);
    }
}

Edit: Crap. This works fine as long as you don't have the Scene and Game views open at the same time. As soon as you can see both of them, though, there is a good chance that OnDrawGizmos() is going to be called during play mode.

-

It's such a glaring problem that I have to assume that it's by design; maybe there's some distinction between editing and editing-while-paused that isn't obvious to me.

My workaround: Avoid the ExecuteInEditMode() attribute and Use OnDrawGizmos() to handle running the script in the editing modes.

// called only during play mode
function Update()
{
    RunTheScript();
}

// called in both normal and paused editing modes but not during play
function OnDrawGizmos()
{
    RunTheScript();
}

The problem with this solution is that it offers no way to execute something in a LateUpdate() equivalent. So if some other objects refer to the results of calculations done by RunTheScript() it's a crapshoot whether they'll get them this frame or the next.