A ghost bone is simply a bone with no group assigned to it.  So in the case of the cape you'd have - Cape 1, Cape2, Cape3, Cape4, Cape5, Cape6.  These would be the groups. Then you'd draw corresponding bones to match those groups. To create ghost bones also, you would then draw a pair of extra bones - maybe as children of the Cape 5 bone - that were for controling the corners of the cape. These bones would be given a name like rCapeCorner and lCapeCorner or something.  The wouldn't have groups.   Then you'd exit the setup room. When adjusting the joints, you'd want to make rCapeCorner and lCapeCorner have groups Cape2-Cape6 as affected actors probably and you'd want to paint their weight influence so that it was strongest in Cape6 and transitioning to weakest in Cape2.

 

Not sure if that makes sense to you. I can make a video of it.