Tutorial on how to set key binds: http://www.renegadesclan.com/modules.php?name=Forums&file=viewtopic&t=1338
Tested and works, quite handy for when you need to tell somone to watch their language or stop bunny hopping.
Wont work using \rcon say "blah blah" but at least your not having to type the whole warning evertime someone breaks the rules, you can just hit one button.
Dont forget to back up your config_mp.cfg file though if you decide to do this.
Nice find!