I think I've figured out how to get custom maps that support Vs to work in Vs, but it's a giant pain in the ass (apparently Valve hates customs...). I have a zip file at
http://www.nine9nine.org/maps/jsarena2.zipYou have to open it up, install the .vpk like normal, you may have to delete the orignal vpk in the addons folder, idk, and then copy the /maps folder into your l4d2 folder
32bit Drive:\Program Files\Steam\steamapps\common\left 4 dead 2\left4dead2
64bit Drive:\Program Files (x86)\Steam\steamapps\common\left 4 dead 2\left4dead2
I was able to change the gamemode on the server and play as inf without crashing, I'd test it with someone else but no one else is online.
I also "fixed" the inf switcher so it's smoother. I can't currently do anything with the multiples of the same inf when there are inf bots yet as that's Valve's fuckup
I also realize none of you fuckers actually check your own clan's forums but this makes it easier for copy/paste.