Yes there is - RDBMS Sync.
docs here: http://www.cisco.com/en/US/docs/net_mgmt/cisco_secure_access_control_server_for_windows/4.1/user/A_RDBMS.html
You'll see a whole load of action codes to add a user, set password, group membership etc. But action 150 sets a static assigned ip address.
It can take a bit trial and error to get it working, but once you get the hang of the syntax its easy and you can easily script the creation of your actions file.
If you have the s/w ACS you can use a csv file, xls or ms access db. You then create a System DSN pointing to the actions db and reference the DSN from ACS. When you initiate the dbsync import it first parses the data then processes it.
Also on the s/w ACS there is a command line to do a parse-only scan of the account actions - try csdbsync -x to get help.