At the moment there are various other programs you can use to get the volume calculations, one that is free and can read in the STL file that you would prepare for 3D printing is MiniMagics, which you can get here: http://software.materialise.com/minimagics
From what few searches I did, creating a command for calculating the Volume of a solid, looks like a lot of work
involving calculus integration of NURBS curves/surfaces...
