If you want to just import simple shapes in a hierarchy, you have to do it with .ase files and import them as textures. This is described in the thread
http://www.alice.org/community/showthread.php?t=570
and I have posted a few simple shapes in .ase format there also.
Since I don't work with a Mac, I can't recommend any 3D object creation program for it, unfortunately. Nor do I know of any file conversion program equivalent to Biturn for the PC. Maybe you could use a school or library PC for a brief time to create your own shapes - 4DBlue (see ref. thread) is pretty small and (for simple things) fairly straighforward - plus it will generate .ase files directly.
Added Notes: Should have done a Google search before posting. There is a Mac version of Wings 3D (
http://www.wings3d.com/), which is a nice free 3D editor - though it doesn't export in .ase format. Blender also has a Mac version, but I find it difficult to use. It does have an .ase export script, though I've never used it.