It cant be done in version 8.2.5, because of two things. There is no Twice NAT capability on ASA. There are individual capability and the second is that if you use an static policy NAT, there is a bug where the ASA does not honor the destination on the ACL (which you need to create) which causes the translation to take place for all traffic.
This is very hard to swallow, however, this is one of the main reasons NAT evolved to what it is now on the ASA.
Mike.
Mike