Ghosts

There is only one way I can think of:

Split the ghost from the household and have them not live in any lot.

You can do that through phone, computer, or Manage Households tab in Manage Worlds.

While yes, it won't return them to the hidden ghost household, they will retain the ghost appearance schedule (appearing at night near their grave or in lots with Spooky challenge or during certain holidays etc). Plus as long as you keep them in My Households tab in Manage Households, you don't have to worry about them getting culled.