Shoutbox

I want to make a plug-in to play a card game with my contacts.
I had design a card system that sends only numbers to the other contact.
I´m using the ReceiveNotify, but the problem is that, the information that i send next to the Notify char is also shown in the chat window, and i don´t want that to happen.
Is there any way in wich i can send hidden information, between boths computers...
Thanks,
    Manu