Well, I don't have an example of my own, but the technique is showcased here.
https://www.youtube.com/watch?v=lLXOBhnL7is Go to the 3:25 mark and see what happens. As the clip progresses you can see the he moves the spearton back, I know it's a bit hard to see with the fancy editing but I'm sure you're sharp enough to see ;). If you pay close attention you can also see the castle archer arrows shooting at it.
I'll also try to explain in words.
The castle archer hits the first thing it targets. You want to make sure it hits the spearton. Once it starts shooting the spearton, you put the spearton in some bizarre place that is far from your other units, like the top of the map. You do this to ensure that the arrows are far away from your other soldiers and to nullify the splash damage.
The idea is that the arrows are still hitting the spearton, if you move the spearton you move where the archer shoots. You have to make sure the castle archer hits your spearton first though. Once he's in position, toggle on his shield wall ability, it blocks 40% of incoming damage and makes him quite tanky.
If you still don't understand I'll send you a replay when I can.