You can get the subtypes from the context by
context.People.OfType<Employee>()
or you can extend the context by a partial class in which you define properties for subtype DbSets:
partial class Context
{
public DbSet<Employee> Employees { get; set; }
}
That's much easier than modifying the t4 template because the standard t4 templates can change in future releases, so you'll have to modify them again.