Hi
I also interested in this topic.
I found a configure around conference following under that.
root@HOSTNAME:/opt/freeswitch/conf/dialplan/default# cat bbb_conference.xml
you shoulde be set up around incomming call to that conference number directly.
at first,make a user account for incomming call as FreeSwitch.
it need specify the autoanswer.
and that call to be transfer to target conference number.
maybe it done.but I'm sorry for my experience is only Asterisk.
FYI: I dont know how is your NAT issue about this incomming call.ok or not.
BR
mack