Did it first time, hah!
You have to get killed while running up onto the platform. It forever locks the platform and there's no way to die to remove that corpse
oh wow! That is a great catch and a complete oversight on my part! Makes total sense! Interestingly, that's the only platform that triggers the turrets in the entire game - i should've looked back at that and made it toggle a barrier like I do in later puzzles. I love when people catch this kind of thing you really only encounter with enough numbers of people testing :)