If you mean hanging clothes, hair and other, ahem... "boneless" things that should swing as the consequence of primary motion, then I suggest you take a look at the Offset section of the user guide, and make it your mantra.
I wouldn't even try with physics in Unity, unless you could delay the reaction of the overridden bones. They wouldn't look natural otherwise. And even then I highly doubt it would look as good as animating them yourself.
