Using a DomainService with CRUD statements (Silverlight)

In my DomainService which is accessing a ADO.NET (.edmx) file I have the following function which returns ALL columns

Public Function GetOpenPOs() As IQueryable(Of PartNumberHistory)
        Return Me.ObjectContext.PartNumberHistories.Where(Function(e) e.OpenClosed = "OPEN PO" And e.NumOfQty = 1 And e.LineItem = 1).OrderBy(Function(e) e.PO)
    End Function

This works great and when I edit the grid and click "Submit Changes" button - everything is saved - works like a charm

Problem is I *want* to only return (and be able to edit) a few of the columns....

I try this function

Public Function GetOpenPOs() As IQueryable(Of PartNumberHistory)
        Return Me.ObjectContext.PartNumberHistories.Where(Function(e) e.OpenClosed = "OPEN PO" And e.NumOfQty = 1 And e.LineItem = 1).OrderBy(Function(e) e.PO).Select(Function(e) e.PO)
    End Function

But get the error:
Error      1      'System.Linq.IQueryable(Of String)' cannot be converted to 'System.Linq.IQueryable(Of BusinessApplication9.PartNumberHistory)' because 'String' is not derived from 'BusinessApplication9.PartNumberHistory', as required for the 'Out' generic parameter 'T' in 'Interface IQueryable(Of Out T)'.

How can I make this work?  The client seeing all of the columns is just overkill

Thanks!