My little proof of concept http://youtube.com/watch?v=wZnFwgkf3mw
extruder based on screw 
Welcome to 2005.
You may want to read through this: http://dl.dropbox.com/u/22464622/A%20History%20of%20RepRap%20Development.pdf
Page Numbered 75 (at the center of the bottom of each page) is relevant.
Definitely a very fun document. Now I want to try the technique in “Strength of objects made by layered manufacturing.”
I think if instead of leaving a hole all the way through, you filled it every 5 layers or so, you could add very sturdy interconnects between layers. They might be good to fill corners with.