Maybe Zilal or Spuzzum, or one of the other people who's experienced with area-based MUDs has a better answer.
My answer probably wouldn't apply here, since I have an online creation system which allows me to create creatures simply by dropping them into rooms and forgetting about them -- they save only once; if they die, they're gone until the room is loaded again.
I think Zilal has online-creation too, but I'm not entirely certain.
One way you might try doing it is having a proc that locates a bunch of mobs at world.New(), and works something like this:
And continue creating mobs that way until you have them in all the areas you want.
Maybe Zilal or Spuzzum, or one of the other people who's experienced with area-based MUDs has a better answer.