I think you're forgetting the obvious solution of having tons of preloaded magazines strapped to you.
Single button magazine ejection, slam your Uzis down onto fresh 100 round magazines. Bonus points for an automated system that moves the next set of magazines into the perfect arms length position at your side for the next reload.
Two handed reloads are for chumps when you are fighting zombies. You would be the guy I'm standing behind to give me that extra few seconds while they're busy eating you. That way once I finish off your attackers I can pick up your freshly loaded (but unspent) gun. And triple-wield!!