you can add your custom parameters with ProviderAttributes, and you can do so by adding new attribute to your provider element in the web.config e.g.
After you do so you can extract them by accessing the ProviderAttributes hash table in your provider e.g.
object value1 = ProviderAttributes["CustomAttribute1"];
object value2 = ProviderAttributes["CustomAttribute2"];
object value3 = ProviderAttributes["CustomAttribute3"];
If you have any other questions don't hesitate to post them here.