Windsor-like Xml configuration <include> in Unity

Question

Hello,

I have common DI configuration for my application and integration tests.

However, a couple of the dependencies do differ; e.g. my IEMailGateway in the integration tests uses a decorated version so that 'real' e-mails are not sent.

In Windsor I would have the 'main' configuration xml file and simply add an include to add the varying bits, like so:

<include uri="file://windsor.extension.xml" />

Now how can I achieve the same thing with Unity?

Regards, Eben