As DM, I'll have you roll the dice, tell you if it succeeded or not, and then have YOU describe what happens based on the roll.

But with this particular thing, it's not really about the story. It's the player trying to maximize their bonuses so the dice will be more favorable. In which case, sure. You can dual wield your hands. But you're still taking a penalty with your off-hand unless you have the feat that removes it. You ever try to punch someone with your non-dominant arm? You definitely take a penalty IRL, unless you're ambidextrous.