Creating form inside of closed brep

Hello,
Does anyone know how I could create a 3D form like in the photos inside of a wall/closed brep using Grasshopper?
Thanks in advance
human-bird-bone-comparison-541 Screenshot_2.1

Or its most recent implementation (I guess, both belong to the same author David Stasiuk):

http://www.bespokegeometry.com/2015/07/22/cocoon/

Thank you for the help, I’ll check it out.