Available here: l4d2-viewmodel-lag-plugin[github.com]
The downsides:
1. Enabling this plugin prevents you from connecting to VAC-secured servers (not ever going to change, that's just how external plugins are)
2. Lookposes and run animations are broken (will be fixed soon)
It's a client-side plugin, meaning you can play singleplayer, join your friend's game, join community/non-VAC servers and still be able to see sway. It also won't affect anyone in your lobby if you're the host, other players have to install it on their side to see it.
The upsides compared to my mod/jigglebone method:
1. Works with any reanimations/remodels without manual adaption
2. Configurable, sway strength and delay are adjustable