How to mix inheritance strategies with JPA annotations and Hibernate?

According to the Hibernate Reference Documentation it should be possible to mix different inheritance mapping strategies when using Hibernate's XML-Metadata:
http://docs.jboss.org/hibernate/stable/core/reference/en/html/inheritance.html#inheritance-mixing-tableperclass-tablepersubclass

However, the corresponding section of the Hibernate Annotations Reference Guide does not cover that:
http://docs.jboss.org/hibernate/stable/annotations/reference/en/html/entity.html#d0e1168

On the other hand, the JavaDocs suggest that mixing inheritance strategies should be possible. For instance in javax.persistence.DiscriminatorColumn it says:

The strategy and the discriminator column are only specified in the root of an entity class hierarchy or subhierarchy in which a different inheritance strategy is applied.

The following is an example for the mapping I'm trying to achieve. I'd like to use table-per-subclass mapping near the root of the hierarchy, but change to table-per-class-hierarchy mapping near the leaves. Here's some example code:

@Entity
@Inheritance( strategy = InheritanceType.JOINED )
public abstract class A implements Serializable
{
    @Id
    private String id;

    // other mapped properties...
}

@Entity
@Inheritance( strategy = InheritanceType.SINGLE_TABLE )
public class BB extends A
{
    // other mapped properties and associations...
}

@Entity
public class BB1 extends BB
{
    // other stuff, not necessarily mapped...
}

@Entity
public class BB2 extends BB
{
    // other stuff, not necessarily mapped...
}

@Entity
@Inheritance( strategy = InheritanceType.SINGLE_TABLE )
public class CC extends A
{
    // other mapped properties and associations...
}

@Entity
public class CC1 extends CC
{
    // other stuff, not necessarily mapped...
}

...

What I expect from this mapping is having exactly 3 tables: A, BB, and CC. Both BB and CC should have a default discriminator column called DTYPE. They should also provide all columns necessary for all mapped properties and associations of their respective subclasses.

Instead , the class hierarchy seems to use the table-per-subclass inheritance strategy throughout. I.e. I get an own table for each of the entities mentioned above. I'd like to avoid this, since the leaves of the class-hierarchy are extremely light-weight and it just seems overkill to have a separate table for each of them!

Did I overlook something? Any advice is highly appreciated! I'll be glad to provide additional info...