First step is to make sure you have the "Skip Trader Mut" installed. If you don't then check out this guide: http://www.speedrun.com/kf09/guide/2flzd

The easiest way to skip the trader in the fastest time possible is to bind the command to a button. For example I have my SkipTrader bound to Q. To do this you type into the console "set input q SkipTrader". Once this has been done, when the last zed dies at the end of a round keep pressing q to skip the trader as soon as possible.

If you have any other questions you can contact me through my links provided on my profile.