Did some digging online and the secret is a dish of moist O²-rich soil inside a loosely sealed clear tote. The clear tote lets the leaves photosynthesize while maintaining a higher than average temp and humidity. Meanwhile the oxygenated soil helps with root production.
The mix I used here is: 1 part fast draining soil mix 1 part sphagnum moss
I used a hose sprayer to moisten/oxygenated the soil every few days. The process took about a month for root development, and I lost 2 props in the process. Heat helps here, I'm in USDA zone 5b and I kept them shaded under my jade tree and a canopy in the yard.
These plants are very cool and seem to be easy to grow, if you have a mature-enough specimen for propagation, use the oldest and lowest leaves for propagation, as they likely produce the least from photosynthesis and will have the stiffest/hardiest stems.
I like this daring approach to getting more plants! Also had to look up 'zombie leaves' and apparently they are sold as plants by themselves. From an ag extension school in NC::
Some, but not all, plants can be propagated from just a leaf or a section of a leaf. Leaf cuttings of most plants will not generate a new plant; they usually produce only a few roots or just decay. Because leaf cuttings do not include an axillary bud, they can be used only for plants that are capable of forming adventitious buds.
Fiddle, are you capable??