Hi,
As per your requirement , you can use the FQDN acl in the class map ACL and then apply the Rate Limiting policies:-
https://supportforums.cisco.com/document/66011/using-hostnames-dns-access-lists-configuration-steps-caveats-and-troubleshooting
http://www.cisco.com/c/en/us/support/docs/security/pix-500-series-security-appliances/91790-pixasa7x-traffic-mgt.html
Thanks and Regards,
Vibhor Amrodia