You've been watching the original 'Buffy the Vampire Slayer' movie haven't you?
I used to do that for fun while on a field trip at the end of my first year at university - there was a grassy field outside the research centre which was ideal to play on - and no walls to destroy
As to teaching good posture in ukemi, perhaps having tori come in to attack uke immediately after the throw may sharpen up uke's senses to the importance of strong posture?
Ruth