I'm having a bit of a stab here but I'd say that it's not possible . The PIX will see this a land attack and not pass the traffic( sho logg will show the exact fault). I would think that you are probably going to be better off if you have a your internal/DMZ DNS point to the DMZ address, This makes better logical sense IMO then trying to go out the firewalls external interface to go back the DMZ.
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...