Linq to Sql Many-One relationship

I have 2 views in SQL set up:

• PurchaseOrder
• PurchaseOrderLineItems

These have many columns aliased (the tables they view/join are not sensibly named... it's a 3rd party product)

I have 2 classes (simplified below)

    class PurchaseOrder    {        public string PoNumber { get; set; }        public string Vendor { get; set; }        public DateTime DateCreated { get; set; }        public IEnumerable<PurchaseOrderLineItems> LineItems { get; set; }    }

and

    class PurchaseOrderLineItems    {       public string PoNumber { get; set; }       public string Name { get; set; }       public double Price { get; set; }    }

I'm using Linq to Sql - with XML mapping file (created with help from sqlmetal.exe)

What I want to do is effectivly populate the IEnumerable in PurchaseOrder with records from the PurchaseOrderLineItem view - effectively joining the tables

I wanted to do this using POCO - without having to add EntitySet<> to my class, as eventually, I will change my ORM to something like nHibernate (which has bag attribute i believe...?)

Currently, I've got a stored procedure - sp_getPurchaseOrderLineItems which takes the PONumber, and then returns a list of PurchaseOrderLineItem objects, that i then add to my result set (this is far, far from ideal)

is there any way I can do what i need? So that basically, a query on PurchaseOrder returns an already populated IEnumerable of LineItems within the instance?

It's worth mentioning that this will only ever be read-only, we'll never be inserting / updating data using this.