Can I add a discriminator via a custom code first convention?

Question

I add a discriminator column to all my entities in order to facilitate soft delete.

Currently I do it by specifying it on each entity one by one:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
   modelBuilder.Entity<Foo>().Map(m => m.Requires("IsDeleted").HasValue(false));
   modelBuilder.Entity<Bar>().Map(m => m.Requires("IsDeleted").HasValue(false));
   //etc etc
}

What I'd like to be able to do is specify it as a Custom Code First Convention. My entities all inherit from a ModelBase class. So I can create a custom convention to map to stored procedures like this:

modelBuilder.Types<ModelBase>().Configure(m => m.MapToStoredProcedures());

but this is not available:

modelBuilder.Types<ModelBase>().Configure(m => m.Requires("IsDeleted").HasValue(false));

So, is there any way to add a discriminator to all entities that inherit from ModelBase other than doing it one by one?