Role management

 Hello,
 I am doing a management of roles for users. At the beginning every user will have only one role. I haven´t used role provider because I don´t want to add a new record into the database. I just want to add roles and when I restart the application, with the global.asax file will be assigned roles that I had at the beginning. How can I do to add roles during the execution?
 Using Roles.AddUserToRole() function doesn´t work because role provider is disabled.
 I use this sentence in Global.asax:
                string[] difRoles = new string[1] { "administrator" };

                HttpContext.Current.User = new System.Security.Principal.GenericPrincipal(User.Identity, difRoles);
But if I use this sentence in execution is not working.
Do you know what sent ...