Slabs in the sulfur cube should make the top of it walkable.

For example, a movable platform could be used; slabs could be placed on the sulfur cube, making its top surface walkable, but due to its properties it could also be moved and have changes in weight, etc. This would be used primarily as a mobile parkour platform, but it might also be possible to sticking together to make a larger platform that could also be fitted with blocks and perhaps entities This would make mobility in Minecraft even more complex and allow for creative exploration in ways never before seen in the game, such as: attaching the platform to the Happy Ghast to create a small mobile base, or doing parkour where you have to jump onto the platform before it sinks.