EclipseLink 2.3 does not support an ON clause. You can only do this in a native SQL query, or through defining a query key.
EclipseLink 2.4 (and JPA 2.1) will have support for an ON clause. You could try the latest 2.4 build.
2.4 only provides ON support in JPQL and Expressions, not yet Criteria. But you can mix Expressions with Criteria using JpaCriteriaBuilder toExpression/fromExpression.