Today me and friends have been playing with this twist on Versus mode. We are only 4, so we usually have 3 guys with the survivors and 1 with the zombies... which inevitably doesn't last long. Also because there's less normal zombies around, as we play L4D modded to have less of them but headshot-only... so the guy stands out.

So we gave him some director powers, without just going for the simple "z_spawn mob".
In short, here's what this does:
Numpad Multiply = spawns a zombie, with long cooldown (2.2 secs)
Numpad Enter = rage mode, you spawn zombies faster (0.3 sec cooldown) but after a few seconds you die (you can spawn like 10)
Numpad Minus = screams alarming all zombies in the area, taking away 50% health

sv_cheats "1"
z_hunter_health "250"
z_exploding_health "250"
z_mob_spawn_max_size "10"
z_mob_spawn_min_size "15"
z_mega_mob_size "30"
bind KP_enter "furia"
bind KP_multiply "crea"
bind KP_minus "corsa"
alias salvo "bind KP_multiply velox"
alias salve "bind KP_multiply crea"
alias crea "z_spawn; bind KP_multiply none; play player\hunter\voice\miss\lunge_scream_end_1; wait 220; play player\PZ\voice\hurt\ZombieDog_Hurt3; bind KP_multiply crea"
alias furia "echo furiainizio; fadein 0.5 255 10 10 (); salvo; alias salva salvo; play player\tank\voice\yell\Tank_Yell_02; wait 500; play player\PZ\voice\hurt\ZombieDog_Hurt3; alias salva salve; hurtme 10000; wait 100; alias salva salve; echo furiafine"
alias velox "echo veloxinizio; z_spawn; bind KP_multiply none; play player\boomer\voice\warn\Boomer_Warning_01; wait 30; play player\PZ\voice\hurt\ZombieDog_Hurt3; salva; echo veloxfine"
alias corsa "nb_rush; hurtme 125; play player\hunter\voice\warn\Hunter_Warn_10"