Nice to see such hacks in tmu too
I think its done by placing the blocks higher then planned in the editor and then change the block height in a hex editor. This way it detects 2 blocks at the same height.
The problem would be to find the correct value in the gbx file.
But i think that if you create 2 almost the same files with the only difference in it the block height then you can easely find the correct value
This way it might even be possible to get dirt high up in the air i gues
Edit : Apparently tt IS possible . In the movie zooz has different heights on the grass
(And i never new about the sliding
)