This still feels like a messy hack to get around oracle shortcomings
that means hibernate or the developer code has to jump through hoops.
From a point of cleanliness it would be prefereble to not have to resort
to a JTA callback and then be able to hide freeTemp call through an
upcoming hibernate callback api (as previously mentioned).

The problem comes down to the issues of obtaining a clob/blob pointer
into the DB which the oracle jdbc driver provides 2 mechanisms for - 
1) either through a ResultSet or Statement (non-prep) executing and
interrogating the resultset.
2) or using a temporary Clob - which is simpler and less intruisive
however hits you with the overhead of resorting to callbacks to free the
temp storage.

(apologies for stating the obvious)

Would it be possible to code scenario 1) as implied below ? - and hide
that code in the user defined type? This means we need a reference to
the session and current object we are trying to persist.

<<snip>>
foo = new Foo();
foo.setClob( Hibernate.createClob(" ") );
s.save(foo);
s.flush();
s.refresh(foo, LockMode.UPGRADE); //grabs an Oracle CLOB
oracle.sql.CLOB clob = (oracle.sql.CLOB) foo.getClob();
java.io.Writer pw = clob.getCharacterOutputStream();
<<snip>>