Note that it's not possible to solve this in a perfect way because:
The knife slashing animation is executed locally and instantly
The Lua script required for the animation is executed on the server. It will be delayed by your current ping value in milliseconds.

So it will always look stupid at least for those people with a "high" ping.

And before someone asks me to add locally executed client-side Lua scripts: Won't happen.

It would drive the complexity into insane new levels. Tons of new commands (for everything but client-sided) would be required. And of course it's a mega huge security risk allowing super easy mega cheat development. It's absolutely not an option. It would destroy CS2D even more.