rockm

"Living things can be influenced to do things that are against their nature. Bonsai, for example"

No. They really can't. If it's not in their nature, it usually won't happen. Bonsai is NOT against a tree's nature, anyway. It is part of it. We are exploiting an existing natural reaction in plants when we use bonsai techniques. Nature "bonsais" trees all the time, whether through harsh weather or animal browsing. Trees developed the capability to dwarf their foliage and rejuvenate themselves by growing new shoots after they're damaged in response to what nature throws at them. We simply do it "artistically."

I'm afraid that trying to manipulate roots to accept grafts to become branch bearing trunks could be difficult, as root and top growth are two different types of plant tissue. To "convert" one to another requires a hormone signal. We can "tell" top growth tissue to produce roots with rooting hormone. I don't know if there is a hormone available that signals root tissue to become top growth.

Cypress knees do not produce bud growth. They have no latent resting buds, as the trunk and branches have. However, neither does plant scar tissue, yet it can be grafted onto in a manner similar to what you're describing. BC growers have thread grafted branches onto the scars around large trunk chops to produce branches where none would appear otherwise. This, however, is above ground growth.

Plants have no epidermal layer. Animals have epidermal layers to their skin. Plants are different. They have cambium underneath their bark. Underneath the cambium is phloem and xylem. You cannot think of plants in animal terms. They do not work the same way.

For what it's worth, extremely nice BC bonsai with similar taper can be made without using knees.