Right, i was not sure about that but makes sense come to think of it.
I guess you would have to settle with using type attributes.
See if you can use user_usertype and then extent that (not sure if that will work but this attribute is available in f16)
# seinfo -xauser_usertype
sesearch -ASCT -s user_usertype | grep user_usertype
sesearch -ASCT -t user_usertype | grep user_usertype
If that does not work the way you like then i guess youll have to use type attributes to implement something similar (or use templates) by your self
If you want to clone the user_t user login domain then why not just clone that module, rename it and extent it?