Item Has To Ship In Two Boxes


I've started helping fix and maintain a website using primarily cs.cart, and was asked a shipping question today that I'm not sure of the answer for (website isn't my main position, I'm just doing what I can to help). We have several products that require two boxes to ship. What is the best way to configure this so shipping rates are charged accurately? At the moment, the only options on a product page are these:

Weight (lbs) :
Free shipping :
Shipping freight ($):
Items in a box :
Box length:
Box width:

Box height

I'm not sure how to put in a second box - At the moment it's just set to the bigger of the two, but that means we're eating shipping costs on the second box.

What are the options here?

Thank you