As others stated before me this is not yet available (not even in 8.3.2, at least it's not in the Release Notes). However, it is possible to run a DynDNS Windows client on a PC/server on the inside network that will supposedly accomplish the trick.
This may or may not be your 'cup of tea', but it may be worth a shot since not much else is available.
Another, less elegant, and probably more expensive solution yould be to use an 'el cheapo' Internet router (the $50 dollar kind available from your local electronic store, wired or wireless) most of which support DynDNS out of the box. You could use this device strictly to handle DynDNS and pass through all other traffic to/from the ASA5505. The ASA would then handle to true firewall duties.
I've not personally tried this but conceptually it should work.
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...
[toc:faq]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 and UDP are I...