That was kind of my thought. You could make it a mini-game for the GM.
Find some automated way for him to generate "spawn points" that he can spend to increase the spawn rates in certain regions. Then the GM can log in every now and then, and spend his spawn points. Give him access to the ruler's channel like Overlord in the last invasion, and maybe one character to move around on his own or something. It could definitely be made into a much more lightweight position. You could have two, one for Monsters, and one for Undead.
