Is there a possibility to use Hiberante with a non-SQL capable datastore?

I'm working in a project where the database access occurs by transfering XML documents between our application and a proprietary datastore. The datastore supports some very basic functions of a RDBMS:

- select, insert, update, delete on tables
- filtering with boolean operators (where clause)
- sorting

Examples of missing featues:

- table joins
- aggregate functions
- DDL
- ...and more

Because the language for datastore access is so limited I think that it is not possible to write a JDBC driver for it. Would there be another way to control the way how hibernate retreives/write data to a persistent storage?

Thanks in advance for any helpful hints..

Rolf