I think I discovered something. If I'm wrong, forgive me. I've linked a video that I made that's a proof of concept.
I call it "Water Casting."
If lava casting is pouring water over lava then water casting is the opposite, poring lava over water.
The trick is to use water vegetation to prevent lava from destroying the water sources. Lava will slowly work its way down flowing water, converting the flowing water blocks into cobblestone and stone blocks.
It's very satisfying to perform. It's easy to do and can be done in survival almost right away. You just need buckets, lava, water, and some sea veggies.
Water casting has some advantages. It's faster, It results in less lag, and you can build into right angles. Water casting gives you a far more predictable, reliable cast. Anyone who has tried to make a big pyramid with lava casting knows that you will get little imperfections due to how lava updates. You can use this process to water cast a pyramid that looks like the square pyramids found at desert temples or that you make for beacons.
I have dozens of more screenshots I'd like to share, and I am happy to answer any questions. Please look at the video I've linked. It's not great but it will give you an idea faster than I type.