Don't use metal. Experiment with soft materials you have, or purchase appropriate items.
If you have any kind of strap that has Velcro closures, that would be useful. Place it right above the little branch on the right side of the split, and pull it secure. It shouldn't be able to slide down.
You could similarly use arborist straps; look at A. M. Leonard online to see what kinds of offerings to get an idea.
Finally, anyone who has had to do physical therapy knows the colored stretchy bands (yellow, red, blue, green) which offer varying levels of resistance. Take one that is stiffest and tie the two sides of the split together (above a side branch that will keep it from slipping).
Worst that can happen? It doesn't work, and you prune it all off anyway. You'll learn some things in the process.
