One way you could do it, if you don't want to decompile the map to easily find out, is to use a point_clientcommand named clientcommand. Set up a trigger_multiple to hit the clientcommand with a:
OnStartTouch - clientcommand - Command - +taunt
Then you can have the trigger_multiple start disabled, and just flick it on and off with a button somewhere, and force all the clients inside to +taunt when they trigger the trigger.