My favourite character ever was a thief-acrobat in 2nd edition. I must have drove the GM nuts with all my crazy stunts, swinging from chandeliers, attempting flying leaps and tumbles and what-not. I would hate to tell a character he can't leap off a balcony and try to land a knock-out blow on the orc captain with the well-placed heel of his boot, just because he didn't choose to be a warrior. I may make it very unlikely but there's a chance...
I would totally let a Thief do that with a simple ability check, then finish it off with a backstab. Same results with narrative flair. A flying leap off a balcony? Why not, don't even bother rolling, you don't need rules for that. Knock-out blow with the heal of a boot. Simple, Non-lethal crit damage after successful "backstab" attack.
Seriously, nothing can't be done by a non-Warrior class that a natural 20 wouldn't cover, or the thief's back-stab.
Remember that this isn't 3e, much-less 4e, where every move is spelled out for you. You don't need hard rules to add flair to DCC RPG combat. Remember that the combat is abstract
. What really matters is if they hit, and how much damage. There could be as many back-flips, round-house kicks, tongues in cheeks and sparkling teeth as you want. It could be in bullet-time and blood could splatter, or not. It's abstract combat in 10-second rounds (it used to be 1-minute rounds in AD&D.) There could be any number of parries and sly exchanges of dialog. Cartoon violence or bloody gore. It doesn't matter. The bad-guy is OUT when he's out of HP. I let my players describe in as much detail as they want.
This is what I mean when I say separate the mechanics from the narrative. Describe your intent, and then roll the dice, and explain what "really" happens after you get the results. That's how I've always done it until I started playing 4e. DCC RPG returns to the good old days of abstract combat.