Yeah how do those other sites have a bot to announce stuff?
You can run an IRC bot as a regular process and it will login to freenode as a normal user. There are many bot programs, but
LambdaBot is one we use our own channel with my friends. It's probably a little more advanced than what you need.
I think you may be able to modify a simple bot program to open a pipe to the IRC process and just write your announcements into it. I found this program,
ii, with which you can do stuff like this:
ii -s irc.oftc.net -n iifoo -f "John Doe"
iipid=$!
# make announcements:
echo "/say Announcement!" > ~/irc/irc.oftc.net/in