SQL> create table t (data# clob);
 
Table created.
 
SQL> declare
  2   buffer1 varchar2(32767) := 'Doesn''t ';
  3   buffer2 varchar2(32767) := 'this work for you ?';
  4   l_data# clob;
  5  begin
  6   insert into t values(empty_clob()) returning data# into l_data#;
  7   dbms_lob.writeappend(l_data#,length(buffer1),buffer1); 
  8   dbms_lob.writeappend(l_data#,length(buffer2),buffer2);
  9   commit;
 10  end;
 11  /
 
PL/SQL procedure successfully completed.
 
SQL> select * from t;
 
DATA#
--------------------------------------------------------------------------------
Doesn't this work for you ?