This recipe shows how you can display one only thumbnail, which launches a multiple pictures slideshow.
The tweak is to display one thumbnail, and to hide the others in a >>comment<< block. The Lightbox slideshow will still find them and display the originals.
Mini:*,-image01.jpg set contains all pictures except the first one.
This will only work in "Lightbox mode 1", with
$Mini['EnableLightbox'] = 1; in config.php. See Hidden2 if you need more than one hidden slideshows and need "Lightbox mode 2".