A walkthrough at last.

[forlik]

Originally Posted by Liz Shaw

You can also throw a fragile object (eg. glasses and cups) at the guard if you aim for his head. But don't try it in MoTMod, for some reason the guards in the other room will investigate the noise...

Originally Posted by forlik

Try to close doors before the guards and select a position to throw as far as possible from the closed door.

It seems the player's position to throw doesn't matter.
I've tried to stun the diplomat's guard from the position between the closed door and the guard on hard difficulty level. After 2nd attempt I've catched a luck