I was thinking about trying barbell hack squats. They are pretty much deadlifts with the bar behind your feet. I'm pretty sure that the exercise would force my torso to remain more upright in the bottom position. I don't see how it could be a dangerous exercise if kept under control...I have never dropped the bar in any exercise, so the possibility of it dropping on my achilles tendons is the same possibility of the bar dropping and bouncing up and hitting my shins during a deadlift.
It's not because I can, but because you couldn't if you tried.