Still work in progress, but I'm thinking of something like this :
http://www.webcamalerts.com/
lets you register, associate a twitter account, checks to see if a particular stream mate girl is online based on their nick.
You can tweet from within it, but I'm writing up all the variations of message at the moment so that the updates will look a bit more random. Then I'll turn on the scheduler so it scans and updates online status automatically.