SQL> BEGIN
  2    EXECUTE IMMEDIATE 'EXPLAIN PLAN SET STATEMENT_ID=''123'' FOR SELECT * FROM DUAL';
  3  END;
  4  /

PL/SQL procedure successfully completed.

SQL>
SQL> SELECT timestamp, depth, operation, options, object_name
  2    FROM plan_table
  3   WHERE statement_id = '123';

TIMESTAMP      DEPTH OPERATION                      OPTIONS    OBJECT_NAM
--------- ---------- ------------------------------ ---------- ----------
14-JUL-05          0 SELECT STATEMENT
14-JUL-05          1 TABLE ACCESS                   FULL       DUAL

MYDBA@ORCL > declare
  2  sql_txt varchar2(200);
  3  begin
  4  sql_txt := 'select * from dual';
  5  execute immediate 'explain plan for ' || sql_txt;
  6  end;
  7  /

PL/SQL procedure successfully completed.

MYDBA@ORCL > select * from table(dbms_xplan.display);

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------

Plan hash value: 272002086

--------------------------------------------------------------------------
| Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |      |     1 |     2 |     2   (0)| 00:00:01 |
|   1 |  TABLE ACCESS FULL| DUAL |     1 |     2 |     2   (0)| 00:00:01 |
--------------------------------------------------------------------------

8 rows selected.

MYDBA@ORCL >