Extending Presence Message

I would like to know if I can extend the USER_JOIN message that gets sent to all the connected clients (in my case I have a flex client) when a new user enters the room.I would like to add custom data like the users address information/email etc from the database to the USER_JOIN message. I can probably do the same by having another IQ type custom message but I am concerned about the bandwidth as now that adds additional messages that need to be sent from each to client to the server. I am wondering if I can add the data to the USER_JOIN message

Any ideas?

Thanks