It is possible to send a message to a specific user (selective push notification) using nowjs and node.js

Question

I have a group a users, all connected to a single server, and I want to send a message from one user to another user, with the receiving user not having to accept any sort of a request from the originating message. So I am trying to use nowjs for this, where I would simply broadcast the msg meant for a specific user, and only the required user would accept it. In short I need to send something like a selective push notification. Do you think this approach of broadcasting is a good idea, as I think I will have max 300 users at once, and if not do have any others suggestions how I can implement this. Thanks in advance.