[Plugin : WooCommerce] – Minimum products

Hi I am making an ecommerce site for a client, what they are after is a website built in the (functional) style of the graze.com site.

The customers should be able to visit the site and select in multiples of 4 how many products they want. The site will be selling cakes etc in boxes, each box with cost a set amount and they are made to contain 4 items, you cannot order more or less in the same box.

Does anyone know any scripts for WooCommerce which might be able to either do this or give a good foundation to try and do this?

Client is after a fast turn around and low budget so any help would be appreciated!

Thanks