My latest experiment is delving into using the boxwrap2d library. I have had, and have been attempting, an idea to create a custom physics object (see image) in which 4 circles are strung together by lines, which all have physics properties. 

I am just wondering how I can create such lines that will work as physics objects that shrink and expand as the circles move. 

In a way it is similar to using Distance Joints to constrain each circle, yet the lines that join the circles would work as physics objects, and interact with other shapes.

The reason for this is that I am wanting to, for example, using it to contain other objects, circles rects etc it can be picked up and bounced around the screen.

Any ideas in how I can pursue this? Many thanks.