Hopefully, someone else who does this can contribute. I have worked with this very little. My understanding is constraints are important, because you don't want joints going in certain directions, because of this kind of thing among other issues.
However, probably you need certain mesh fomations at the joints. You don't appear to have much there at the elbows and knees and the bends are pretty tight. I think you should try putting elbow and knee formations on the mesh. There just doesn't seem to be enough there.

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