I had a long rhomboid quartz rock I wanted to plant a parthenocissus on, but the ends of the rock were too pointed to make it stand vertically or even at a sloping angle. Laying it on its side would have been boring. I bought an epoxy putty product similar to this one (
https://www.amazon.com/Loctite-1999131-Purpose-Repair-Ounces/dp/B000BOB8P6)
I made a flat disc of the putty wider than the rock's pointed end but not so wide it wouldn't fit into a suitable container. I press the pointed end of the rock into the putty and waited till the epoxy cured. After that the rock+putty disc combo could stand on its own and I wrapped the parthenocissus roots around the rock. The end of the roots were forced to flare outward because of the epoxy disc. The whole setup is buried to the tip right now, but eventually I plan to expose it so that only the flare of roots and the epoxy disc are under the soil level. I predict that the flat disc and the flaring roots will give enough stability for the whole setup to remain upright, but I would probably need to wire it in place anyway. I suspect that the rocks in your pictures are all wired down below the soil level. They probably use some sort of cement, like mine, or in the link above. The thick root pad probably provides additional stability.