Your April Fools joke has gave me an idea seeing the pictures. You could, instead of make a gang of hobbits appear with the Arnor power, you can made appear a building from where recruit the hobbits and their 'rocket siege' units, just like how Sauron makes appear his castle.
That could give some units for help Arnor, but how is a tier 2 spell, the building will be surely weak, and must be place somewhere where can be defended if the enemy attacks it.