Hi Robin,
the code handling this is in modules/mod_vm_flexible_zoom_effect/tmpl/default_images.php line 30
<?php // Showing The Additional Images
if(!empty($this->product->images) && count($this->product->images)>1) { ?>
you can see the code is only produced if the image count is greater than 1 .
You would need to add an extra 'if' sequence if (( count($this->product->images)>0)&&(count($this->product->images)<3)) before the above and display what you want then change the above to >3 and make it a elseif.....
something like this should work
Cheers