You could certainly do it that way, by adding morphs to the hip. There wouldn't be any bones in the hierarchy below the hip, if that were the case. You could make the morphs in the cloth room, which is how I did it for Minnie. However, what I'm suggesting here is that if the shirt is really short, i.e. hardly covers the buttock/hip joint, then you may not need to do anything special. You would just include the buttock bones in your set-up as if you were making a catsuit or something like that. You wouldn't need to add any unusual bones (or "body handles"). Hope that makes some sort of sense...