Did you try it? It's hard to tell from the docs if it's possible or not. they mention directories but nothing about individual streams other than to imply that it might be possible. I'd try something like this?

Code:
application.onConnect(newClient,user){
    newClient.writeAccess = "/mystreams/"+user;
    newClient.readAccess ="/mystreams/"+user;
    application.acceptConnection(newClient);
}

Psx