The product.conf file is currently a properties file. It currently supports a single property:
slot=eap (or whatever)
That "slot" property is currently used to determine what module to use when loading the admin-console.
What I describe in the "Establishing Identity" section above could accomplished by simply adding two more properties
identity=Foo
layers=xyz,vuw
This example assumes we have an identity named "Foo" that uses two layers on top of the base, xyz and vuw, with xyz taking precedence over vuw.