Junction table with additional payload columns in EF4 CTP4 Code First

I have the following tables:

WOPartList (defines parts that have 1 or more Part_Size) WOPartSize (defines sizes that have 1 or more Part_Size)

Part_Size (junctio开发者_运维知识库n table as addt payload columns such as sku, on_hand etc...)

Here are the POCO classes for the DAL:

    // Real World Scenario:

    // PartList                Related to Part_Size     Related to PartSize  
    //
    // #8 Stainless Lag Bolt   sku- 87234018            size- 2 x 1/2  
    //                         on hand- 214 
    //                         on order- 12 

    // #8 Stainless Lag Bolt   sku- 87234199            size- 3 x 1/2  
    //                         on hand- 81 
    //                         on order- 18 


    // #10 Stainless Lag Bolt  sku- 87237835            size- 1 x 1/2  
    //                         on hand- 11 
    //                         on order- 14 

    // #10 Stainless Lag Bolt  sku- 87237835            size- 2 x 1/2  
    //                         on hand- 11 
    //                         on order- 14 

    // #10 Stainless Lag Bolt  sku- 87237835            size- 3 x 1/2  
    //                         on hand- 11 
    //                         on order- 14 

    // So the idea is to be able to create a size once and use it many times
    // for many different parts... But I need to keep specific statistics for
    // each size of a part...

    // How do I tell the Model that Part_Size is a many-to-many junction table
    // between WOPartSize and WOPartsList as well ?


public class WOPartSize
{

    public int WOPartSizeId { get; set; }
    public DateTime tadded { get; set; }
    public string size { get; set; }

    // Nav Collections
    public virtual ICollection<Part_Size> Parts { get; set; }

}


public class Part_Size   // Junction Table
{
    public int WOPartSizeMMId { get; set; }

    public string part_no { get; set; }
    public string part_descr { get; set; }
    public string sku { get; set; }
    public decimal cost_each { get; set; }
    public decimal price_each { get; set; }
    public int on_hand { get; set; }
    public int on_trucks { get; set; }
    public int on_order { get; set; }

    // Put ICollections<> here ?

}

public class WOPartsList
{

    public int WOPartsListId { get; set; }
    public DateTime tadded { get; set; }
    public string part_descr { get; set; }

    // Nav References
    public virtual WOPartType PartType { get; set; }
    public int WOPartTypeId { get; set; }

    public virtual ICollection<Part_Size> Sizes { get; set; }

}

How do I configure the junction table ? Annotations ? Fluent API ? My main trouble is getting the additional payload fields in junction table... Otherwise I would simply let EF generate the table for me and have NO POCO class...