This would be pretty easy to implement. You'd just have to go into the script and find where weapon sprites are set up and add a random variable that procs when you attack, and based on the random variable, define alternative weapon sprites for the attack. If not that way, then replace attack with a skill and do the same thing with a random variable when you use the skill, then change the animation according to the variable.
I'll look into this, see if I can't tweak some things.