He explored a JPA-based DAS approach via Fluid which is an Apache Lab project signifying its exploratory approach.
Fluid, through a prototype implementation, establishes the feasibility of such an approach without any modification to JPA.
More information on Fluid can be found at:
- A series of blogs posts where he rambles about it
- Persisting Service Data Object using OpenJPA: Relaxing Type
- Persisting Service DataObjects with OpenJPA
- Fluid OpenJPA implements SDO Data Access API