**Function: Expose Sorting layer & Sorting Id in layer properties in inspector for any kind of renderer. **Usage: put SortingLayerSetterEditor.cs into any folder named Editor, add SortingLayerSetter to a GameObject with a render component attached (SpriteRenderer, MeshRenderer,...). **Disclaimer: I just extracted, learned and customized the code…

SortingLayerSetter.cs

using UnityEngine;
using System.Collections;


public class SortingLayerSetter : MonoBehaviour {

   

}

SortingLayerSetterEditor.cs

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

[CustomEditor(typeof(SortingLayerSetter))]
public class SortingLayerSetterEditor : Editor
{
    private static MethodInfo EditorGUILayoutSortingLayerField;
    protected SerializedObject rendererSerializedObject;
    protected SerializedProperty sortingLayerIDProperty;

    public void OnEnable()
    {
        if (EditorGUILayoutSortingLayerField == null)
            EditorGUILayoutSortingLayerField = typeof(EditorGUILayout).GetMethod("SortingLayerField", BindingFlags.Static | BindingFlags.NonPublic, null, new Type[] { typeof(GUIContent), typeof(SerializedProperty), typeof(GUIStyle) }, null);

        rendererSerializedObject = new SerializedObject(((SortingLayerSetter)target).GetComponent<Renderer>());
        sortingLayerIDProperty = rendererSerializedObject.FindProperty("m_SortingLayerID");
    }

    public override void OnInspectorGUI()
    {
        serializedObject.Update();
        gui();        
    }

    private void gui()
    {
        SortingLayerSetter component = (SortingLayerSetter)target;

        // Sorting Layers
        {
            var renderer = component.GetComponent<Renderer>();
            if (renderer != null)
            {
                EditorGUI.BeginChangeCheck();

                if (EditorGUILayoutSortingLayerField != null && sortingLayerIDProperty != null)
                {
                    EditorGUILayoutSortingLayerField.Invoke(null, new object[] { new GUIContent("Sorting Layer"), sortingLayerIDProperty, EditorStyles.popup });
                }
                else
                {
                    renderer.sortingLayerID = EditorGUILayout.IntField("Sorting Layer ID", renderer.sortingLayerID);
                }

                renderer.sortingOrder = EditorGUILayout.IntField("Order in Layer", renderer.sortingOrder);

                if (EditorGUI.EndChangeCheck())
                {
                    rendererSerializedObject.ApplyModifiedProperties();
                    EditorUtility.SetDirty(renderer);
                }
            }
        }
    }
}