hmm, now that I think of it, the 1 turn delay couldn't work. the dm would just retreat before getting hit. So how about this:
The samurai suffers a -2 penalty on ac, and does the attack roll. If he hits the opponent, the opponent will roll a reflex save:
if the reflex save beats the attack roll by 5 - the attacked creature takes regular damage
if the reflex save beats the attack roll by less than 5 - the attacked creature takes x2 damage
if the reflex save = attack roll - the attacked creature takes x3 damage
if the reflex save is lower than the attack roll by 8 - the attacked creature takes x4 damage
if the reflex save is lower than the attack roll by 9 or more - the attacked creature dies instantly
If the enemy can't roll a reflex save, it will roll a fortitude check, if it suceeds in the save against the attack roll, the opponent will take regular damage, if it fails, the creature dies instantly.
this can't be applied on creatures imune to critical hits and sneak attacks
something like this?