Sketchy-Physics

[firedrake]

Does any one know how to make hollow objects or how to attach objects together in Sketchy Physics without it creating an impenetrable box around them? I am trying to make a pipe that is hollow, or a moveable cart that a ball will fall into, but i can't figure out how to hake hollow objects, or how to attach things together, with out making them into a group. This would help me greatly thanks. Someone please help!