Basically you drop your items across the finish line, then cross it, then pick it back up before you get teleported. The blocks has a tag on it allowing you to place it on certain, but anywhere on the map. using the shears from iron course and the blocks from diamond course you can get out of the normal map area and be able to build a stairway back into the map. I have recorded the full process of breaking it here: (part 1, showing how I got the first items allowing complete freedom to do whatever) (part 2, breaking/editing the Redstone/map)

Good question! Thankfully Moo was able to answer it before me