Couple things you can add is making a default channel and a channel list for the same message.
/massPM This is a mass message
This would make it send a message to all the people in the channel you're already in
/massPM #chan1,#chan2,#chan3 This is a mass message
This would make it send a message to all the people in these channels, as long as you're in them.
Ok I updated the code.