Post a welcome message on "message board" after registration


I have a plugin (post-user-login-update-plugin) which adds an "admin" friend to everyone automatically after registration.

I want to post a welcome message (from the admin user) automatically on the "message board" widget  of the new user after registration. (The message board widget is set on the profile)

I think by adding some simple code to post-user-login-update-plugin.

any help?

Im using v 1.8