I will soon be creating a mod that does this.
It will take the products in the cart, and grab all the products that have ever been purchased with those products, and grab all the products you've configured in the upselling links section of the add/modify product page.
It will then take a random number (which you specify) of those products and display them with a show me more link to take a different random set. You can view the mod at
www.mixtapemp3.com.
The mod will be available when the store opens at
http://www.websitecm.com/