I've been having increasingly better luck at shimpaku cuttings since I started taking them three years ago. I will wait until the tree is completely dormant typically mid to late january here in atlanta. I will then take all the cuttings from the tree, then re-cut them on a cutting board using a very sharp razor blade, in theory to avoid crushing the cambium. Dip them in a powder rooting hormone, then place them in moistened superplugs. A seed type starter tray I picked up from the local hydroponics store. It also has a clear plastic dome with vents on the top, and place to slide a grow light.
The plugs seem to keep the right amount of moisture around the cutting, so I just keep a small amount of water on the bottom of the tray. I then keep the cuttings on my bathroom counter, figuring the extra humidity from hot showers would be good. I've also monitored the temperature in the dome, and it seems to hold around 77-80 degrees with the vents open and light on. At night I turn the light off and shut the vents. The first year I did this I didn't use the plugs or grow light and had only about 15-20% success. Last year around 50%. And this year probably closer to 75%. Now I have to figure out what to do with all these shimpakus.
An added bonus of using the superplugs is that you can lift the inner tray that holds the plugs from the outer shell which holds the water, and then see which plants are rooting, without really disturbing the plant. Then you can take the ones that have put out sufficient roots and pot them in whatever media you would like.