Something

   nua_handle_t *handle;
   sip_to_t *to;
   to = sip_to_make(NULL, "sip:me@remote.machine");
   if (!to)
      return;
   to->a_display = "tata";
   handle = nua_handle(nua, this, SIPTAG_TO(to), TAG_END());

   if (handle == NULL) {
      printf("cannot create operation handle\n");
      return;
   }

   nua_invite(handle,
              /* other tags as needed ... */
              TAG_END());