Why a private message? And whats wrong with using OperServ's LOGONNEWS to send the message?
An alternative is a bot (would have to be opered so it could receive connect notices) that one receiving a connect notice sends the message.
I would advise the message be sent as a NOTICE not a PRIVMSG since according to the IRC RFC nothing is supposed to automatically reply to NOTICE's but are free to automatically reply to PRIVMSG's. Which could cause loops between whatever sent the PRIVMSG and who it's sent to.