Finally had these made today!  This is the first design I had in mind.  It is the easiest one to machine and the weight savings are quite good.

If you want to read about the different designs go here: Spacer Design
Picture 5942
Surprisingly the 10mm spacer came out weighing less than the predicted weight by .6 grams. 
Picture 5927
Comparatively a 10mm plain carbon fiber spacer weighs in at 5.2 grams. 
Picture 5934
Here are the weights of the 20mm and 5mm spacers respectively.
Picture 5930 Picture 5931
And here’s how they stack up. 
Picture 5924