For those who want to play Left 4 Dead Versus in Advanced or Expert.

NEW!!

(Thanks to Kev3056 for this workaround)

You can play L4D Versus (any difficulty) on the current patches by following these steps:

1. Host a versus lobby, but don't start the game
2. Bring up the developer console (~)
3. Type z_difficulty x (replace x with Easy, Normal, Hard, Impossible. Hard is Advanced and Impossible is Expert)
4. Change server to a local game
5. Play!