When zoning something when you load another game or scenario, or you start a new one, that zoning is still on the mouse pointer. For instance, you can load the Splitsville scenario, select the Wellspring of Unsavouriness, load your own game at year 0, and place a Wellspring of Unsavouriness. This works for any building that is available in any game (including all Special Buildings). Note - You must still pay for the building.