That sounds like a reasonable suggestion, my only problem with it is that it seems to imply that My module is either a subclass or part of or some how affiliated with Net::IRC, when in reality they have nothing at all in common (except for possibly connecting to IRC).
If you're worried about subclassing considerations, how about something like Net::IRCTool::BotName? This creates a new level called 'IRCTool' for IRC Tools to use, and BotName is whatever you name your module (maybe Net::IRCTool::BUU). It also leaves the door open for other people to release other IRC Tool modules, without causing confusion that something like Net::IRC::Tool or Net::IRC::BUU would cause.