As long as you're talking about Opt-in Faxing Only... and automatically Faxing...

I would recommend contacting the Fax services in the link I posted...
http://www.savetz.com/fax/

With Software and related Services...

There just may be some Hidden Features available in a few of those Fax Services that might Do the Job...

Or ways that a Software Freelancer can Tweak a Possible Solution...
http://www.allfreelance.com/

Phil