Are you in Kentico 8 or 7? If 8 then yes I think you could do this. In 8 you have a lot of flexibility around the shopping cart and checkout process. You could add another webpart to your shopping card that would display related products based off the latest product added or related to all the items in the cart. You would still have to do some custom programming to make this happen, but basically you could loop through the ShoppingCartItemInfo Provider and create a dataset of related products and tie to the webpart.
If you are in 7, you could probably mimic the same, but it would be more complex process. In that case I would recommend reaching out to support and getting some assistance on what would be the best practice to make this happen.