I've seen Lithops grown the same way with their roots dangling in water.
Just in case you don't already know, I don't
grow "semi-hydroponically" or any other term for just aggregate. I use soil, that being the stuff you find in the ground. Technically this is a mixture of clay, silt, and sand which I then mix with coarser material to maintain aeration.
Many cacti and succulents, including the difficult ones like Ariocarpus, Turbinicarpus, and Lithops are often found in incredibly dense clay soils but I can't really mimic that in my climate. I feel that "just the rocks" is a poor substitute for actual soil, perhaps in the same way that Ariocarpus used to be kept alive by not watering them; it works but it is far from ideal