If I understood you well, you don't want to show additional images, but you want to show them in slide show, when you open large main image.
Well, you get addtional thumbnail images, when you name the main image like this.
- YourMainImageName.jpg ( this one is main image )
- YourMainImageName_01.jpg ( this one is additional )
- YourMainImageName_02.jpg ( this one is additional )
and all of this images should be in the same folder.
Example: Images/yourfoldername/
To enable showing large images in slide show with Fual Slimbox,
you should have the same images in folder:
images/large/yourfoldername/
-YourMainImageName_01_LRG.jpg ( additional image to show )
-YourMainImageName_02_LRG.jpg ( -"- )
Now try this ( I didn't try it so I don't know exactly if this works, but this is just an idea )
So IF you want to kill thumbnails, you delete additional images associated with your main image, but leave images in images/large/yourfoldername/
with suffix LRG.
If you use imagehandler 2 I think it will automatically make the same, but optimized images in it's cache folder.
I hope the first part will be helpfull to PaulK too.