Apparently Congress could do so and have it pass judicial muster =>
http://www.freerepublic.com/focus/f-bloggers/3276464/posts?page=13#13
For some reason the link you posted keeps bringing me back to this same thread.
All the hype about 3D printed guns is quite funny when you can make or finish a really nice lower receiver with an inexpensive CNC milling machine. Of course it is cheaper and probably easier in most cases to do it starting with a partially completed lower with jigs and common tools.