Load Navigation Property by its Key - asp.net-mvc

Question

I am using the EF CF approach and have:
the following data model:
public class Category {
[Key]
public int CategoryID { get; set; }
[Required]
public string CategoryName { get; set; }
public virtual ICollection<Product> Products { get; set; }
}
public class Product {
[Key]
public int ProductID { get; set; }
[Required]
public string ProductName { get; set; }
public virtual Category Category { get; set; }
}
the following DataContect definition:
public class EFCFContext : DbContext {
public EFCFContext() : base("EFCFConnection") { }
public DbSet<Category> Categories { get; set; }
public DbSet<Product> Products { get; set; }
}
The purpose of this code is as follows:
I have an ASP.NET MVC 4 application. There is a form for editing the Product entity, and a "lookup" selector/editor for the Category entity bound with the Category.CategoryID property.
When submitting the form to the corresponding HttpPost Action, the Product.Category.CategoryName is still empty. I do not have a direct instance of the Category object in this scope:
//Category cat = new Category();
//cat.CategoryName = "Fake Name";
//context.Categories.Add(cat);
//context.SaveChanges();
EFCFContext context = new EFCFContext();
Product prod = new Product();
prod.ProductName = "Fake Name";
prod.Category = new Category();
prod.Category.CategoryID = cat.CategoryID;
//prod.Category.CategoryName is null. ModelState Error is added.
context.SaveChanges();
As a result, some Model Validation errors occur.
I need to assign/reload the Product's Category property explicitly, since I already know the CategoryID.
So my question is:
How do I force the navigation property to load by its Key/ID without the extra steps (and thus avoid the ModelState Errors)?
I may be going in the wrong direction. Any guidance will be helpful.