I have the same problem except in my case I have some flammable liquid products which can only ship UPS or FEDEX ground. If there were other products in the order they can ship with the flammable liquids using the ground service. So I would need it set up so that if UPS Ground was "required" for any item, then all items in the order ship together by that method.
Because my store sells various items, I have to live with the several shipping options displaying regardless of whats in the basket. I have notices on the flammable liquid product pages and in checkout warning customers of the shipping restrictions of flammable liquids, yet nearly every order for flammables comes in with the cheapest shipping method selected (usually postal and flammable liquids are a big no-no in the mails).
I experience lots of administrative work contacting these folks and lots of misunderstandings I would like to avoid.