adding user to permission container only

Hi @ll!

I've got a question concerning the feature of LiveUser that it should be 
possible to use existing tables for authentication. I'm using a table 
with many users in which username - password combinations are stored. 
Mapping LiveUser to the right entries was no problem - authentication is 
working fine.
But I don't know how I can add user rights to this users. How can i add 
a user to the permissions container that is already stored in the 
authentication container? If I try the ::addUser method, LieveUser tries 
to add the user to both containers and gives an error message.

Hope you can help me!
Greetings
Christian