Half a year ago, I added vertical half-slabs to Minecraft because no one had done it in a way that I liked. It wasn't great, but now it uses Display Entities instead of Item Frames, and uses a LOT fewer commands.

To get a vertical half-slab, throw any slab onto a Stonecutter (copper slabs must be waxed first). They place similar to End Rods and Amethyst Buds. in that they will attach to the face you click on.

IMPORTANT NOTE:
Worlds using the old version of this datapack are not supported. There is no way to automatically upgrade.
The best way to upgrade an old world to this version of the pack is to destroy all the vertical slabs, update, then replace them. This is due to NBT and CustomModelData changes.