You can do selective NAT with commands such as
ip nat inside source route-map ?
http://www.cisco.com/warp/public/cc/pd/iosw/ioft/ionetn/prodlit/1195_pp.htm
Using a route map, you should be allowed to use access-lists to match as needed.
I could not find a reference to it in the universal CD manual, but I have used it before to do selective NAT.