Meetme - Disabling dynamic conferencing

I have an Asterisk 1.4.0 box connected to the PSTN via a PRI circuit. I’ve designated one of our DIDs for use with meetme teleconferences. The inbound call is routed over to meetme essentially with:
exten => s,1,Meetme()

When a caller connects, they are prompted for a conference number, and if that conference exists in meetme.conf they are prompted for the associated pin. If the conference number does not exist, the conference is dynamically created.

Using Authenticate() prior to meetme() is not an option, since multiple conferences are scheduled at any given time, and although each has their own unique conference number/PIN, they all dial in on the same DID. Not having authentication and allowing anyone to dial in and create a conference is also not an option.

Is there any way to totally disable dynamic conferencing and only allow static conferences?