eg. "For .NET 2.0 C# Adapter Two Class Scenario":
Path = <LLBLGen Installation Folder>\Templates\SharedTemplates\Net2.x\C#
EntityClasses template file = entityUsingDerivedAdapter.template
EntitySubClasses template file = derivedEntityAdapter.template
Take care that this will affect other template classes that's using (referencing) these namespaces.
eg: derivedEntityFactoriesAdapter.template & inheritanceInfoProviderDerived.template
Where you can find the following line in the top of the file:
using <[RootNamespace]>.EntityClasses;
Which should be changed as well to use the same namespace used for your subEntities.