By extending of WCF there are several types of possible extensions in the configuration file. In general there are three main groups of extensions:

1. Behavior Extensions
2. Binding Element Extensions
3. Binding Extensions

Here is an example which can be found in the machine.config file.

Following picture shows how to implement the custom binding.

To do this, it is necessary to implement three different classes, which derive from Binding, StandardBindingCollectionElement and StandardBindingElement.

Read the complete post at http://developers.de/blogs/damir_dobric/archive/2008/07/13/service-model-extensions.aspx