You can do it like this: (Paste in its own section anywhere above main)
[rgss]module RPG
 module Cache
  def self.special_bitmap(filename)
   self.load_bitmap("Graphics/SpecialBitmaps/", filename)
  end
 end
end
[/rgss]
I am not sure how touchy spaces are in path names so I removed it.
Just put your special bitmaps in a SpecialBitmaps folder in the Graphics folder.
Use RPG::Cache.special_bitmap(filename) to access the bitmaps in the folder.
*hugs*
- Zeriab