DuplicationHelpers.cs

using UnityEngine;
using UnityEditor;

// @kurtdekker
// Make sure this is in an Editor folder!

public static class DuplicationHelpers
{
	// duplicates the current object and puts it back right after the original.
	[MenuItem( "Assets/Dupe Here FFS")]
	static void DupeSelectedItemHereFFS()
	{
		foreach( var item in Selection.gameObjects)
		{
			int siblingOrder = item.transform.GetSiblingIndex();

			var originalName = item.name;

			var copy = GameObject.Instantiate<GameObject>( item, item.transform.parent);

			// TODO: do anything clever you want with the name, such as suffix it with +1, etc.

			copy.name = originalName;

			copy.transform.SetSiblingIndex( siblingOrder + 1);
		}
	}
}