To add a custom service to ACS...
Goto "Interface Configuration" then "TACACS+ (Cisco IOS)" and in the "New Services" section enter your new service "nokia-ipso" plus tick the user & group checkboxes. You might need to add "ip" as the protocol depending on what the actual T+ requests look like.
When you next edit a user or group you'll see a new TACACS+ service into which you can enter your custom attributes:
Nokia-IPSO-User-Role=role_name_on_IPSO
Nokia-IPSO-SuperUser-Access=<0|1>
Note that only very basic syntax checks are applied, basically as long as eahc line has somehing=something ACS will not complain, so its up to you to make sure the values are correct.