Ok, here’s what…
Since I’m an ambidexterous dude (really) and we’re running low on paper for dual wield print here, lemme point out that there is no magic mushroom that can make you run @ full speed & shoot two different, moving targets at the same time, nevermind the bursts you (ok, we all) want.
Now, for most of the tasks that require freedom of both the hands, you’ll still need both; I know we all love the arcade and Lara Croft’s sideboob and arse, but your character, really, does it this way: whilst firing from a twin USP, if one weapon empties and you assume it before you first squeeze the trigger so you hold a clip in the opposing hand, still you need to stop firing the other gun, too.
What does this tell you?
First of all, don’t try to poke your gun with an upright standing clip on the table and fire away. Especially don’t if you’re doing it with Christopher Walken sitting against you, firing against you. He knows you’ll crush, he’s co-written the script. 
Now about that panic, and wielding multiple sidearms @ once; can it be just something special, like having that shotgun ready if you’re facing an overwhelming number of Zs? I’m seeing it this way, you can get really hurt and have some beers to ease the trouble, you can snort your way around Brutes and Hulks with coke and meth, you can cook creatures from other planes of existence in your pot, but you’re never ever gonna draw two handguns even if fifteen Zs are in your face trying to eat it anytime now.
I’m only starting off creative, code a panic button in game; it has a certain treshold, some additional messages to display (hints, for ex.) and an extra feature or two until it wears of, like +2 or so on attacks with firearms until it wears off. And again, if you have your other single-handed weapon holstered.
