Can I have Both Product Listing only AND shopping cart functionality work in the same shop?

Hi,

This might seem like a weird request, but I have a multisite where I am trying to make it so that users (shop owners) can choose whether they want to just display a product or have it for sale, on a product by product basis instead of on a whole shop by shop basis.

Is there a semi-simple way to do this type of thing? Or can you point me in the direction of where I can start poking at the code?

Thanks
Lisa