Configuring custom database with Liferay

We are looking at using Liferay with our own homegrown database. We have written our own dialect class for this. Following how other databses are configured, this is what I have done:

1. registered the db as a datasource using jndi in tomcat (modified web.xml and context)
2. modified portal-ext.properties to specify the database and dialect

This just doesn't seem to work- looking at the Liferay sources, specifically com.liferay.portal.dao.db.DBFactoryImpl, the call to getDB does an instanceof check with a fixed set of dialects. This fixed set obviosuly doesn't contain my custom dialect and so the portal doesnt launch successfully.

My question is:

1. Is what I am trying to do (using custom db with dialect ) at all possible in Liferay
2. If it is, what am I doing wrong?

Any help/comments will be most appreciated.

Thanks.

If you're so near to Liferay source that you have been able to write a class replacing some native one, why not build the source and then you have that class there? This is not the nicest solution, but one that came to my mind when nobody else seems to know what to do with this.