If you want use Sauron’s Influence, you must retreat back into to the own base or to the targeted building. This is not a problem with Necromancer form. He has the teleport ability for move across the entire map.
But Gorthaur or Sauron(with one ring) move very slowly across the map and they can't use teleport.
So, I have smaller idea for Sauron's Influence ability:
Theoden/Grima can use the Cruel Taxes ability for a farm anywhere on the map.
I think that Gorthaur and Sauron should have the same system for Sauron's Influence. So, you only need click to targeting building. I think that these two forms should be primarily on the battlefield and not traveling across the entire map for use the influence on building.