Why don't you ground layer it? Build a wall around the exposed roots and fill with soil. A plastic container split & then taped back together after filling would work. The adventitious roots seen in your picture will grow into the soil, as will others that will form, and you can then feel quite comfortable severing the stem at the existing soil line, your main concern being good support while the new root system establishes anchoring for the plant.

Al

Hm, I get it. Sort of like building a false soil line, letting those little visible roots grow in, and then perform my surgery, all the while keeping the new soil line? So I already have established roots before I do my surgery, and I can just replant where I need to? I'll have to do some looking online to see how to rig up the plastic container, but this is a great idea, and one I never thought of! It's kind of like a "sewing machine" moment, like when the inventors of the sewing machine were trying to make the thread follow the needle, like in traditional sewing- it took a clever person to see that the eye of the needle could go in the tip, instead of the far end! :) Thanks, Al!

Its done quite often. Here's one link from Google,

Jane

Here is a link that might be useful: Air-layering

Yes, you have it. Ground or mound layering and stooling are very effective propagation techniques. They require a little more effort than cuttings, but as hobbyists we usually don't worry about that so much when the technique is sure to yield a higher % of successes. Besides, I'm thinking you want to take advantage of anything that moves you closer to a sure thing, and an established root system w/o having to wound, (as is the norm in air layering) goes a long way toward reducing the stress of separation.

Since you understand dedifferentiation and redifferentiation, you'll appreciate it's likely that tissues in the old stem will reorganize into a new apical meristem after separation & you'll end up with a twofer out of the deal.

Here is a tree that had a trunk too tall for good bonsai. I'm shortening it by several inches, using a ground-layering technique:
{{gwi:2042}}

I cut a hole a little bigger than the trunk, then made a vertical slit up the sidewall, and then continued it across the bottom to the hole. I applied a tourniquet on the trunk (you won't need one because of the preformed adventitious roots), slipped the split pot over the trunk from the side, taped it back together, filled it with soil, and kept it moist.

Al

Wonderful! The link, and the picture, were incredibly helpful! I used a deli container, cut a hole, slipped the whole thing around the plant, and added substrate. I made sure the roots were actually tucked in nicely, and watered.
{{gwi:100083}}
How long would you estimate I wait to check? Days, weeks, months? Is it possible to wait TOO long, or will the roots just become more robust the longer you wait? I'll keep this updated if anyone cares to follow, and I assume I'll need more advice when it comes time to perform my little surgery as well. Thank you very much for your help. Man, I love this forum! :D

About the time you see roots curling around the inside of the plastic container is a good time to separate. I'm guessing 2-3 months, but a lot depends on how favorable cultural conditions are. If it's warm enough & the plant was growing well for you prior to the layering, it will take less time than if your plant was stressed and just limping along. Just so you're not too anxious - ground layering a plant that so readily produces adventitious roots is pretty much a slam dunk.

Al