There is no option that I can see that will allow access to a basic ServiceHost to load a configuration config section from an external source.
And there is no way that I can see that you can update or replace the system configuration in runtime (plus it doesn't make sense to change a config in a web app).
Your best option is to build a class that represents your different configuration options e.g. which binding and which security and so on. you can then save that class to an xml file using a serialization process. When a connector loads you grab the associated xml and deserialize it and build the service Host / Client Channel using pure code, should be fairly easy.
See Custom Service Host.
And for the client side just use a ChannelFactory.
Worst option is to use the OutOfTheBox element classes from System.ServiceModel.dll and implement half the WCF library on your own.