There is no 'special bone' for capes -- none of the base models have them so why would there be one? There are a few techniques you can use to weigh a cape. They all look fairly bad, but sometimes you can get it looking... less bad.
Some people will simply weight it to the torso to make what's called a 'cardboard cape,' where it deforms around the shoulders but not at the bottom. Another technique would be to weigh the bottom of the cape to the legs or feet to give it the appearance of moving with the body.
However you decide to do it, though, it won't look realistic. Thus is the failure of capes with these games.