EF 6 - Cascade Delete on one to many without backreference

I have something like this:

public class Gadget {
  public int Id { get; set; }
  public string Name { get; set;}
  public int SuperHeroId { get; set; }
}

public class SuperHero {
  public int Id { get; set; }
  public virtual ICollection<Gadget> Gadgets { get; set; }
}

Notice that while a Gadget is "owned" by a Superhero (and therefore there's an FK in the database), my domain model does not have a hard reference in that direction.

When I delete a superhero I would like to also delete all their gadgets. How would I do this?

My research indicates that if I had that reference it would be something like

mapping.Entity<SuperHero>()
  .HasMany(x => x.Gadgets)
  .WithRequired(x => x.SuperHero) //this is the part I can't do
  .WillCascadeOnDelete();

but as noted, that doesn't work with my domain model.