Rdlc SubReport issue, Cant use the List(of Object) Property from objectdatasource in report or subreport

I am trying to create an RDLC report in VB.net 2008 using object datasource.

The thing is, my object datasource is a list of Item objects. Each Item object has a property named Stock - which is a list of ItemStock objects. The main properties of both classes are as follows:

Item Class:
Name,Id, Stock,<and some other like MRP,Tax etc.>

ItemStock Class:
BranchId,BatchNo,Expirydate,StockQuantity

A single Item object can contain a number of ItemStock items for each BranchId. The Item.Stock property will be therefore the union of such stock items, i.e. List( of ItemStock).

Now, my report named Stock report will have a List(of Item) object as a datasource(binding source). I get the required object list with no error at all. I assign the list to a Datagrid to display branchwise aggregate stock values. That is:

Itemname         Branch1    Branch2   Branch2
item1               12         2         3

This works fine, as I have used LINQ to get the sum of stock values for item in each branch, by handling the Cell_format event

But the problem arises when I create a report. My report needs to be in format:

Item1 Name
     Branch     BatchNo   Expiry      Quantity
     Branch1    12677     12/09/2009    56 
     Branch1    1217      04/04/2010    6 
     Branc开发者_开发问答h2    22644     12/03/2011    16 
     Branch3    72600     12/02/2012    7 

Item2 Name
     Branch     BatchNo   Expiry       Quantity
     Branch1    2677     12/09/2009      5 
     Branch2    244      12/03/2011      1 
     Branch3    7200     12/02/2012      7 

Now I can't understand how to use the property Stock on an Item object to display this report. I have an option of using a subreport, which I created. But I can not figure out how to assign the stock property of particular item object while processing the subreport.

I also tried handling SubreportProcessing event as follows:

  Private Sub SubreportProcessing(ByVal sender As Object, ByVal e As SubreportProcessingEventArgs)
        e.DataSources.Add(New ReportDataSource("Chemasis_BusinessObjects_Objects_ItemStock", ctype(itemBindingSource.Current,Item).Stock))
    End Sub  

But obviously, this takes the first item in ItemBindingSource and so, all the stock values are displayed as the same.