The WCF team gave us hooks to override service creation so its an acceptable MS practise. It seems to me that RoleEnvironment is responsible for instantiation of the RoleEntryPoint classes, but there are no hooks provided currently:
http://social.msdn.microsoft.com/Forums/en-US/windowsazure/thread/f109484e-3694-47d9-932a-cb89469936f9

I've looked at the code for RoleEnvironment and I don't think it would be too hard to allow us to supply a custom RoleEntryPointFactory to override a default. Currently there are work arounds but would be good if the containers "just worked".