Shoutbox

How are you going to send the pressed keystrokes to the contact?
You need to open an external connection for that.
For that you need to know the IP address of the contact.
For that you need to send something to the contact (file transfer, etc) as Messenger doesn't always use a direct connection which would reveal the IP.
For that you need to work at protocol level (sniffing).

Note: the (!IP) command, or any other method of sending the IP to your contact so his script knows your IP is of no use as that would require the script to send your IP to everybody who you talk to as it can not know who has the script and who doesn't.

AKA: certainly not strait forward to make something like this.