I used to be "effdeevee"---FDV---...but I couldn't use that username again. That's right...now, I'm BronxFigs. Glad I bugged you! You (Dave,...not, Cecil) just cost me 60 clams!
The stainless-steel method worked for about three years, until I forgot to water my trees, and I lost two of the three that were screwed together. The remaining tree survived, and is doing well without the partners. The bark started to fuse where contact was made, but upon reflection, Dave's method will work much better because the unlignified stems are much easier to manipulate, bend, and twist. If the trees live, and I'm sure they will, they will eventually fuse together. Growing in-ground will reduce the waiting time to a couple of seasons, especially if you let them grow rampant. Trim them back to shape later. I used screws because I started with stems that were fully lignified, and unbendable. Softer stems will work better.
By the way, this method is used to fuse dozens of seedling (Ficus-Banyan), or, Trident Maple together so they will develop short, but very fat trunks, and eventually are sold as Bonsai. Of course they are trained to resemble larger trees in the process. I've seen this done with Olive trees also.
This method can be exploited with trees that need pollinators to set fruit. Think, two apple whips twisted together, or, pears...etc.
You have a good memory.
Frank