Combining products into one e-commerce store

Hello all,

What is the easiest/best way to get multiple products with different shipping costs to show up in the same store so that they can be processed in a single transaction? Now, this may seem confusing so here is a little background information to help put my question into context.

We offer several publications that customers can purchase, with a tiered shipping cost associated. However, we also offer a publication that is completely free; and no shipping costs. We frequently have customers that order both types of publications.

Because of Convio's system, shipping costs (tiered) can only be applied to stores, not products. Therefore, I must create two different stores for each of these publication types. It would be a pain for my customers to have to make two separate transactions if they wanted both publications. Is there another way I can do this? Any suggestions would be greatly appreciated. Thanks!