Discussion thread here:
http://forums.bistudio.com/showthread.php?152431-Discussion-about-stances/page2
I'm Sneakson on the forums as well so contact me if you would like to.
The Playstation controller has pressure sensitive buttons and actually the harder you pressed the buttons the more higher you would go and on a keyboard this would naturally be impossible to simulate but if it was bound to the mouse this could also be possible.
NEW: Here's a video of the only way to peek over short obstacles right now and the animation is superbad:
http://www.youtube.com/watch?v=0CQ6KjTWuEk