We use this in a slightly different environment.
Concrete we have a web application, and we want to inject a class
("OurDataAccess") that is kept in our WAR file into a self written ODA
driver.
The ODA driver is packaged into the BIRT plugin folder, so it is found
by the BIRT classloader. However we want to avoid to deploy
"OurDataAccess" twice, especially as it is not kept in a plugin project,
but in a standard Java project instead.
Our solution was to tell BIRT to search along the classpath of the
parent classloader (concrete that's the web-app classloader). That's
what the setting in the config.ini file means.
You should find this config.ini in your BIRT runtime installation folder
- at least it is part of the BIRT runtime download.
Hope this clarifies my idea, however I'm not sure if it fits your
concrete situation.