With Scattershot being the only Archery skill for effective CCing, what would then be an effective way of dealing with Stun immune enemies when you are playing solo?

I'm not sure what the number of cc options you have correlates with dealing with cc immune enemies.  If he's immune, even if archers had 20 cc options they'd be in the same boat.
 
As far as the question goes, I think kiting would be the best option you've got.

I see. I guess archers will always need a tank after all.