How do I override the default isolation level when using the Transaction attribute in Spring.Net
[Transaction( IsolationLevel.ReadUncommitted )]

<object
  name="HibernateTransactionManager"
  type="Spring.Data.NHibernate.HibernateTransactionManager, Spring.Data.NHibernate32"
  dependency-check="none">
  <property name="DbProvider" ref="MsSqlDbProvider"/>
  <property name="SessionFactory" ref="SessionFactory"/>
</object>