Possibility for Nested Inheritance

It would be great if Doctrine had the possibility to define a further inharitance in a subclass.

Example:
There is a class DataObject managing things like created- and lastedit-
timestamps, archiving objects before updates, ...
One of the sub-objects is Content.
There are several types of content.
Written directly to a database field, read from a textfile on server,
executed php file on server, loaded from another server via xmlrpc and
so on.

I'd like to use a single table inheritance to map all information of
the different content objects in one table.
If I understand the model right the only alternate solution would be
to write each single content object to the discriminator map of
DataObject.