I'm not really sure if I'm following you correctly. You don't want to edit index.php. If you want the code for the slider, you can open includes > helper-slideshow.php. Unfortunately, I can't help you about automatically inserting all your latest products on the frontpage slider.
What I'm suggesting is to create a page called for example "Latest Variable Products", then on the that page insert the related images for each Variable Products and link them to their respective single product page. Go to Template Builder > Insert the slideshow element then select the "Latest Variable Products" page. Other than that or editing the slideshow which I can't help you with, I doubt if there is an easier way.
Anyway, let me tag the rest of the support team to help you out. :)