well provided you find a way to determine if a key is pressed (maybe $editbox on a timer?) you wouldnt have to send each keypress only the first. then when the recieving end gets the msg it echos it and waits for a msg from that person resetting a variable. The of course the next time they type the cycle repeats. I usually type quite fast however and can send multiple lines alot (not to mention pasting) so i still think youll get flooded off.
Since it already requires both parties to have the same script why not use sockets and make your own protocol for it?
its a nifty feature but i think its cost may be too great (unless you find a way using sox or something in wich case id use it lol)