namespace Main
{
    public class WorkDb : DbContext
    {
         private DbModelBuilder _modelBuilder;
         public Entities() : base("connectionString")
         {
         }
         public SetEntityMap<TEntityMap, TEntity>() : where TEntity : class
                                                                            where TEntityMap : EntityTypeConfiguration<TEntity >, new()
         {
              modelBuilder.Configurations.Add(new TEntityMap());
         }
         protected override void OnModelCreating(DbModelBuilder modelBuilder)
         {            
               _modelBuilder = modelBuilder;
               _modelBuilder .Configurations.Add(new HomeMap()); 
               base.OnModelCreating( _modelBuilder );
         }
    }
}

namespace Other
{
    public class LoadOtherEntities()
    {         
         WorkDb.SetEntityMap<BookMap, Book>();
    }
    
    //... Описание классов Book и BookMap
}