The main problem is this can't be done the way rocket coded the zombie animations & fsm.
You can slow them down, but they will never walk with their arms out like classic Zombies should. He wanted "28 Days Later" and "Resident Evil" style fast sprinting Zombies because I am sure he thought it would make it more challenging...
Aww shame. I really wanted to have a mission beeing hard as hell, but not because of bandits. But because of millions of zombies chasing you through Cherno, giving no shits about walking slow inside etc. I like having DaiZy missions as close to MP aswell. BUT, I also like mods and different things. :3