You can't seem to scale wall objects (the pieces just implode / explode apart from one another). The best you could do is lower it down into the ground so it's not so high.
There are however a few wooden scenery pieces that you can scale, but you would have to look through them to see if you could find something that fit the bill and then build your wall piece by piece through duplicating and placing the individual objects.
Unless someone else has better knowledge on how to scale walls
