Did you try using the fake GI preset in carrara or other studio light setup w/ no GI?...ambient occlusion? Many other lighting options to also try. If you get results you like w/ baking try that.(baker plugin).The fact is GI just takes longer.Yes, you can choose to have lights only effect certain objects, but I don't really think that will help render time significantly if at all.

No need to think outside the box....
    Just make it invisible.