Strictly speaking it has been always possible in Code First Migrations because you can run sql in a migration:
public partial class AddIndexes : DbMigration
{
private const string IndexName = "IX_LogSamples";
public override void Up()
{
Sql(String.Format(@"CREATE NONCLUSTERED INDEX [{0}]
ON [dbo].[Logs] ([SampleId],[Date])
INCLUDE ([Value])", IndexName));
}
public override void Down()
{
DropIndex("dbo.Logs", IndexName);
}
}
But I realise that you are probably actually asking if you can create an index using the IndexAttribute introduced in 6.1, but with an Include column - the answer to that is "No"