this would also make an awesome trainer option
i think this would be kinda difficult to do.
try this, and make your own: www.autohotkey.com/
the forums are great, and you can get help on allmost every topic over in the irc-chat, too.
as an explanation what that is: its an systemwide scripting engine, that works in games, too.
you can define a trigger (key or other) and create a script that should be executed.
if you watch the speedrun for "Portal" on www.speeddemosarchive.com you will see this program in action.
one of the guys who did a speedrun used AHK (auto hotkey) to automaticly backward-bunnyjump.