Need to recognize CNG/T38 and then hangup

We have a SIP trunk and are using freepbx System is up and running and placing scheduled outbound calls. There is a specific requirement to auto-detect if a number dialed is picked up by a fax machine/voicemail/human. AMD can certainly cover the last two. How can I best add a check for fax as well? I do not believe that I want to enable fax detect in sip.conf as that will route the outgoing call to fax extension in dialplan if CNG or T38 detected. I do not wish to do that. I wish to simply set some userfield data in CDR and hangup.