Solution 1:

Here is how I just got EF 4.1 (RC) to do table splitting in Code First.

  1. Define your two entities. Make sure to include the key in both entities. Also, include navigation properties in each entity pointing to the other entity.
  2. In your OnModelCreating override . . . a. Map both entities to the same table. b. Create the relationship between the two tables.

        modelBuilder.Entity<EntityOne>().ToTable("MySingleTable");
        modelBuilder.Entity<EntityTwo>().ToTable("MySingleTable");
    
        modelBuilder.Entity<EntityOne>().HasRequired(p => p.NavToEntityTwo).WithRequiredDependent(c => c.NavToEntityOne);
    

This is working for me, but realize that given the newness of the RC I've only been able to look at limited and simple scenarios.