There is not a way to clump your products inside the shopping cart. However, there is a work around.
1. Make a new department, possibly the 'Product Department'. Under 'Departments' choose 'Add Department'
2. Create content pages for the 'Product Department' using the products to clump. Set creative headlines and teaser copy for the products (this will be the only information the viewer will see).
3. Use the 'Alternate URL' field to redirect the urls from the product department to the page the products are found in the shopping cart. (Viewers will see the headline and teaser copy and when clicked, instead of going to the article page they will be redirected to the shopping cart page.)
4. Create a new clump that takes content from the 'Product Department'. For a tutorial on setting up a clump, please visit www.membergate.com/clumps