Association of Subshapes with labels

Hi all,

I'm working with the OCAF framework and would like to store additional information on subshapes in sublabels. The setup is similar to the following:

ShapeLabel -- TNaming_NamedFace
|
Face1Label -- TNaming_NamedFace
| |-- Extra_Attribute
|
Face2Label -- TNaming_NamedFace
|-- Extra_Attribute
...

I want to be able to interactively select the subshapes (faces in particular) and associate them with the corresponding label. I'm already able to select subshapes using an open local context on the main shape.
Do I have to store an TPrsStd_AISPresentation for each sublabel? If so, how could I avoid this and only create the sublabel and attributes on demand?

Regards,

Björn