I am opening a wholesale site, for clothing items, and intend to sell some items in lots only. But I want the customer to be able to select different types of the product to make up their case lot.

For example:
T-shirt "A" is sold in lots of 10 only. BUT you can mix up the sizes in the order like so:
5 size Small + 2 size Medium + 3 size Large= 10 total items in the lot.

Is there a way to customize the buy box or something (like with multiple quantity boxes) so they can put how many of each size they want to make up their lot of 10? I am using Zen Cart v.1.3.7