customized asterisk VOIP call like a call back

we have two asterisks A and B, asterisk B is located behind a VOIP firewall and can not accept incoming call but can send outgoing call. the incoming calls to asterisk A should be terminated by asterisk B, When an incoming call arrives to A, it should hold it and send a request to B, the asterisk B get the request but hangup it as it can not complete incoming calls and originate the call toward asterisk A, and Asterisk A connects this call from Asterisk B and held call, to avoid FAS ( False answer supervision ) the held call in asterisk A should not be answered until the other leg arrives from asterisk B.