Can I send a message to a player who isn't it my campaign?

I put up a LFP for my Song & Ice game and quickly got players.  I got more players than 6 that I think is the top end of the ideal party size.  I can send easily messages to the players in my campaign.  I want to send a message to the one fellow saying that while I'm currently full, I'm going to keep on a "wait-list" in case a place opens up.  How do I send a message to someone not in my campaign?

Unfortunately, at this time the only way to message someone is through their profile. Please bear with us as the message boards have been recently revamped and they are a work in progress.  You might want to try to search for the user in the forums. If they have ever posted you can find them that way.  - Gauss