Добавил: The DSystem
This is Missmgish's idea. She wasn't sure on how to put it together so I helped out.
Since Gamebanana couldn't handle the size of this mod, I uploaded to mediafire and the file is simply the link to the concert mod.
Place this into the following directory:
Steam > steamapps > common > left 4 dead 2 > left4dead2 > addons
Below is a video showing the mod:
(If no video window is shown, click here)