It would need a bit of tweaking, but if you have the Data Explorer plugin installed you could create a modified version of the " Who has been sending the most messages in the last week?" query to only report for TL0 users and then run it every so often to see who’s sending a lot of messages.
If you wanted you could even add to the query to generate a report showing relative volumes of messages vs posts for a user, e.g. Fred has sent 25 messages and not posted any topics/replies.