you may 
1. to the insert using a procedure.
   write an exception (dup_val_on_index)
   something like

      BEGIN
          insert into mytable(...)
      exception 
          when dup_val_on_index then
              insert into anothertable_Notconstrained (...)
              -- or use utl_file to write the violated records into a OS file.
     END; 
2. use a simple insert statment.
   create a triggger on base table which does the same stuff above like the procedure.