TLDR: How do I turn off ecommerce for specific sites?

I have several websites some are just for marketing that link to my ecommerce stores and two are ecommerce stores.

There are two different stores geared toward different but similar markets, I want some products to be listed only on one of the stores, and others to be listed on both. For products that only need to be listed on one store, it's easy enough to set the "Website" under the ecommerce settings in the sales tab of the product entry. I can also have products show up in both stores by just leaving that field blank, however here's the rub, if I don't specify a website, then the sitemap will generate entries for these products on my marketing(non-ecomm sites), which google and the like will then crawl and index, which is not what I want. 

How can I disable e-comm altogether for only some of my websites?