Insert User into People Picker Column who is not part of SiteCollection

SPSecurity.RunWithElevatedPrivileges(delegate()

                {

                    SPListItemCollection myColl = SPContext.Current.Web.Lists["Test People Editor"].Items;

                    SPListItem item = myColl.Add();

                    SPUser user = SPContext.Current.Web.EnsureUser(pplUserName.Accounts[0].ToString());

                    string strUser = user.ID.ToString();

                    SPContext.Current.Web.Update();

                    item["UserName"] = strUser;

                    item.Update();

                });