message moderation question

Hello,

I have been trying to set up an ezmlm list so that we can moderate
messages.  What we would like is to be able to moderate all posts by
subscribers and reject all other posts.  The EZMLM doc. hints that this is
pointless, but it's really the most useful application of message
moderation.  Has any list member done this?  I see that some third party
commercial support folks have done it:

"Customized Kavi Mailing List Manager switch. The -y switch is used to
create the -mOuy combination that rejects public posts and moderates
messages from all other senders. 'Subscribers can post, all others are
rejected,"

We can't figure out how they did this.  Can anyone help us with this?

Thanks in advance.

John