Composite Key with EF 4.1 Code First

I am trying to figure out how to have a composite key using EF code First 4.1 RC.

Currently, I am using the [Key] Data Annotation, but I am unable to specify more than one key.

how would one specify a composite key?

Here is my Example:

 public class ActivityType
{
    [Key]
    public int ActivityID { get; set; }

    [Required(ErrorMessage = "A ActivityName is required")]
    [StringLength(50, ErrorMessage = "Activity Name must not exceed 50 characters")]
    public string ActivityName { get; set; }

}

I need the "ActivityName" to also be a key. Sure, I can code around this, but thats not good database design.