The pieces in the OP pic are about as solid of chunks as I've ever seen. They tend to be fragile, splintering away at a mild flex. They are cactus skeleton after all. Then of course my experience with it is confined to the stuff you find in the wild that's been exposed to the weather since it died.
If you could find some stout pieces, or even cut a live cholla (pronounced like choiya, BTW) and cure it in a sheltered environment, it might be possible to treat it with tung or linseed oil or similar to make it last longer, but it will still rot away fairly quickly, and you'd only have about a foot or so to work with. It might last you 5 years tops at a guess, if it doesn't break before that.
5 years is long enough to coax some ficus roots, but the conditions to accelerate that process will also speed the process of decomposition.
I guess I'm saying it's an interesting idea to use it as a scaffold that's intended to rot away eventually, but it might not work out as well as you'd think.
BIt what the hell, I'm willing to send you the pest pieces I can get my hands on if you send me some cuttings or the like. We can see what climate does to it maybe.